Export tariffs are far less common than import tariffs.

The author's explanation of how deep events occur would be most weakened if which of the following were discovered to be true?

A．Deep events are far less common than shallow events.

B．Deep events occur in places other man where crustal plates meet

C．Mantle rock is more ductile at a depth of several hundred kilometers than it is at 50 kilometers.

D．The speeds of both P and S waves are slightly greater than previously though.

GM Organisms

By far the most common genetically modified (GM) organisms are crop plants. But the technology has now been applied to almost all forms of life, form. pets that glow under UV light to bacteria which from HIV- blocking "living condoms" and from pigs bearing spinach(菠菜) genes to goats that produce spider silk.

GM tomatoes first appeared on British supermarket shelves in 1996 (a different fresh GM tomato first appeared in the US in 1994), but that the consumers were in favor of GM technology did not erupt until February 1999. This was because a controversial study suggested that a few strains of GM potatoes might be toxic to laboratory rats. Those experiments, subsequently criticized by other experts, were carried out in Scotland by biochemist Arpad Pustzai.

What followed was a European anti-GM food campaign of near religious fervor. Spearheaded in the UK by environmental groups and some newspapers, the campaign would have far-reaching consequences. It culminated in an unofficial moratorium (延期付款)on the growth and import of GM crops in Europe and led to a trade dispute with the US.

GM crops are today very rare in Europe, strict labeling laws and regulations are in place for food (DNV = A bar codes), and public opinion towards the technology remains largely negative. Several UK government reports have offered qualified support for GM crops and produce, though they argue that the economic benefits of the technology are currently small. Some African nations have also opposed engineered crops, even to the point of rejecting international food aid containing them.

GM produce has been taken up with far less fuss in the US (where it does not have to be labeled), India, China, Canada, Argentina, Australia and elsewhere. However controversy over a type of GM corn --only approved for animal feed--which turned up in taco shells and other products stirred opinion in the US.

Biotech Revolution

The human race has methodically improved crop plants through selective breeding for many thousands of years, but genetic engineering allows that time-consuming process to be accelerated and exotic traits from unrelated species to be introduced. But not everyone agrees this represents progress.

The root of genetic engineering in crops lies in the 1997 discovery that soil bug Agrobacterium Tumefaciens can be used as a tool to inject potentially useful foreign genes into plants. With the help of that microbe, and other gene-implantation technologies such as gene guns, geneticists have developed a multitude of new crop types.

Most of these are modified to pest, disease or herbicide resistant and include: soya, wheat, corn (maize), oilseed rape(canola), cotton, sugar beet, walnuts, potatoes, peanuts, squashes, tomatoes, tobacco, peas, sweet peppers, lettuce and onions, among others. The bacterial gene Bt is one of the most commonly inserted. It produces an insecticidal toxin that is harmless to people.

Supporters of GM technology argue that engineered crops -- such as vitamin A-boosted golden rice or protein-enhanced potatoes -- can improve nutrition, that drought -- or salt-resistant varieties can flourish in poor conditions and prevent world hunger, and that insect-repelling crops protect the environment by minimizing pesticide use.

Other plants have been engineered to improve flavour, increase shelf life, increase hardiness and to be allergen-free. Geneticists have even created a no-tears onion to banish culinary(厨房的) crying, and novel caffeine-free coffee plants.

"Frankenfood" Fears

Critics fear that what they call "Frankenstein foods" could have unforeseen, adverse health effects on consumers, producing toxic proteins (and allergens) or transferring antibiotic-resistance and other genes to human gut bacteria to damaging effect. But there has been little evidence

A．Y

B．N

C．NG

GM Organisms

By far the most common genetically modified (GM) organisms are crop plants. But the technology has now been applied to almost all forms of life, from pets that glow under UV light to bacteria which form. HIV-blocking "living condoms" and from pigs bearing spinach(菠菜) genes to goats that produce spider silk.

GM tomatoes ,first appeared on British supermarket shelves in 1996 (a different fresh GM tomato first appeared in the US in 1994), but the consumer furore that surrounded GM technology did not erupt until February 1999. This was because a controversial study suggested that a few strains of GM potatoes might be toxic to laboratory rats. Those experiments, subsequently criticised by other experts, were carried out in Scotland by biochemist Arpad Pustzai.

What followed was a European anti-GM food campaign of near religious fervor. Spearheaded in the UK by environmental groups and some newspapers, the campaign would have far-reaching consequences. It culminated in an unofficial moratorium(延期付款) on the growth and import of GM crops in Europe and led to a trade dispute with the US.

GM crops are today very rare in Europe, strict labeling laws and regulations are in place for food ( DNV = A bar codes), and public opinion towards the technology remains largely negative. Several UK government reports have offered qualified support for GM crops and produce, though they argue that the economic benefits of the technology are currently small. Some African nations have also opposed engineered crops, even to the point of rejecting international food aid containing them.

GM produce has been taken up with far less fuss in the US (where it does not have to be labeled), India, China, Canada, Argentina, Australia and elsewhere. However controversy over a type of GM corn -- only approved for animal feed -- which turned up in taco shells and other products stirred opinion in the US.

Biotech Revolution

The human race has methodically improved crop plants through selective breeding for many thousands of years, but genetic engineering allows that time-consuming process to be accelerated and exotic traits from unrelated species to be introduced. But not everyone agrees this represents progress.

The root of genetic engineering in crops lies in the 1977 discovery that soil bug Agrobacterium Tumefaciens can be used as a tool to inject potentially useful foreign genes into plants. With the help of that microbe, and other gene-implantation technologies such as gene guns, geneticists have developed a multitude of new crop types.

Most of these are modified to pest, disease or herbicide resistant, and include: soya, wheat, corn (maize), oilseed rape (canola), cotton, sugar beet, walnuts, potatoes, peanuts, squashes, tomatoes, tobacco, peas, sweet peppers, lettuce and onions ,. among others. The bacterial gene Bt is one of the most commonly inserted. It produces an insecticidal toxin that is harmless to people.

Supporters of GM technology argue that engineered crops -- such as vitamin A -- boosted golden rice or protein-enhanced potatoes -- can improve nutrition, that drought -- or salt-resistant varieties can flourish in poor conditions and stave off world hunger, and that insect-repelling crops protect the environment by minimising pesticide use.

Other plants have been engineered to improve flavour, increase shelf life, increase hardiness and to be allergen-free (see also: hay fever-free grass). Geneticists have even created a no-tears on ion to banish culinary(厨房的) crying, and novel caffeine-free coffee plants.

"Frankenfood" Fears

Critics fear that what they call" Frankenstein foods" could have unforeseen, adverse health effects on' consumers, producing toxic proteins ( and allergens ) or transferring antibiotic-resistance and other genes to human gut bacteria to damagin

A．Y

B．N

C．NG

In a quiet，darkened lecture room，you begin a frustrating fight against fatigue. The overhead projector hums，and you cannot concentrate on the slides. You stop absorbing information and become absent-minded. The professor lost you a long time ago. You are bored.

Virtually everyone gets bored once in a while. Most of us chalk it up to a dull environment. “The most common way to define boredom in Western culture is‘having nothing to do. ’”says psychologist Stephen Vodanovich of the University of West Florida. And indeed，early research into the effects of boredom focused on people forced to perform. dull tasks，such as working a factory assembly line.

But boredom is not merely an natural property of the circumstances，researchers say. Rather this perception is subjective and rooted in aspects of consciousness. Levels of boredom vary among people：some individuals are far less liable to boredom than others-and some，such as extroverts(性格外向者)，are more likely to have this feeling.

Thus，a new generation of scientists is coping with the psychological interpretations of this most tedious of human emotions-and they have found that it is more complicated than is commonly known. Researchers say that boredom is not a unified concept but rather comes in several flavors. Level of attention，an aspect of conscious awareness，plays an important role in boredom，such that improving a person's ability to focus may therefore decrease boredom. Emotional factors can also contribute to boredom. People who are poor in understanding their own feelings and those who become sucked in and distracted by their moods are more easily bored，for example.

Staying away from tedium is not easy. People who are liable to boredom are more likely to suffer from ills such as depression and drug addiction；they also tend to be socially awkward and poor performers at school or work.

The purpose of the first paragraph is to______.

A．illustrate why people are less able to focus

B．show how boring a lecture in a dark room is

C．tell people how fatigue affects concentration

D．describe a situation where people can get bored

In a quiet，darkened lecture room，you begin a frustrating fight against fatigue. The overhead projector hums，and you cannot concentrate on the slides. You stop absorbing information and become absent-minded. The professor lost you a long time ago. You are bored.

Virtually everyone gets bored once in a while. Most of us chalk it up to a dull environment. “The most common way to define boredom in Western culture is‘having nothing to do. ’”says psychologist Stephen Vodanovich of the University of West Florida. And indeed，early research into the effects of boredom focused on people forced to perform. dull tasks，such as working a factory assembly line.

But boredom is not merely an natural property of the circumstances，researchers say. Rather this perception is subjective and rooted in aspects of consciousness. Levels of boredom vary among people：some individuals are far less liable to boredom than others-and some，such as extroverts(性格外向者)，are more likely to have this feeling.

Thus，a new generation of scientists is coping with the psychological interpretations of this most tedious of human emotions-and they have found that it is more complicated than is commonly known. Researchers say that boredom is not a unified concept but rather comes in several flavors. Level of attention，an aspect of conscious awareness，plays an important role in boredom，such that improving a person's ability to focus may therefore decrease boredom. Emotional factors can also contribute to boredom. People who are poor in understanding their own feelings and those who become sucked in and distracted by their moods are more easily bored，for example.

Staying away from tedium is not easy. People who are liable to boredom are more likely to suffer from ills such as depression and drug addiction；they also tend to be socially awkward and poor performers at school or work.

The purpose of the first paragraph is to______.

A．illustrate why people are less able to focus

B．show how boring a lecture in a dark room is

C．tell people how fatigue affects concentration

D．describe a situation where people can get bored

By far the most common snake in Britain is the adder. In Scotland, in fact, there are no other snakes at al. The adder is also the only British snake with a poisonous bite. It can be found almost anywhere, but prefers sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all.

Most people regard snake bites as a fatal misfortune, but not all bites are serious, and very few are fatal. Sometimes attempts at emergency treatment turn out to be more dangerous than the bite it self, with amateurs heroically, but mistakenly, trying do-it-yourself surgery and other unnecessary measures.

All snakes have small teeth, so it follows that all snakes can bite, but only the bite of the adder present any danger. British snakes are shy animals and are far more frightened of you than you could possibly be of them. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislikes intense ly. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are very close.

The effect of a bite varies considerably. It depends upon several things, one of which is the body-weight of the person bitten. The bigger the person is, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will al so have better resistance against the poison.

Very few people actually die from snake bites in Britain, and though these bites can make some people very iii, there are probably just as many cases of bites having little or no effect, as there are of serious illness.

Adders are most likely to be found ______.

A．in wilder parts of Britain and Ireland

B．in Scotland and nowhere else

C．on uncultivated land throughout out Britain

D．in shady fields in England

By far the most common snake in Britain is the adder. In Scotland, in fact, there are no other snakes at all. The adder is also the only British snake with a poisonous bite. It can be found almost anywhere, but prefers' sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all.

Most people regard snake bites as fatal misfortune, but net all bites are serious, and very few are fatal. Sometimes attempts at emergency treatment turn out to be dangerous than the bite itself, with amateurs heroically, but mistakenly, trying do-it-yourself surgery and other unnecessary measures.

All snakes have small teeth, so it follows that all snakes can bite, but only the bite of the adder presents any danger. British snakes are shy animals and are far more frightened of you than you could possibly be of him. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislikes intensely. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are close.

The effect of a bite varies considerably. It depends upon several things, one of which is the bodyweight of the person bitten. The bigger the person, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will also have better resistance against the poison.

Very few people actually die from snake bites in Britain and though these bites can make some people very ill, there are probably just as many cases of bites having little or no effect, as there are of serious illness.

Adders are most likely to be found ______.

A．in wilder parts of Britain and Ireland

B．on uncultivated land throughout Britain

C．in shady fields in England

D．in Scotland land nowhere else

Drug use among teens concerns many people in California. Advocates of the "Stop Drugs Now" program, which was piloted in public schools in five California counties last year, argue that the program should be used throughout the state to decrease drug use among teenagers. Which of the following statements, if true, would most strengthen the argument of the advocates of "Stop Drugs Now" that the program should be expanded statewide?

A．School programs are far less important than parental messages in influencing a teenager's decision to use drugs.

B．Drug use among teens in the five counties where the "Stop Drugs Now" program was piloted has been dropping steadily for over a decade.

C．Teenagers at the public schools where the "Stop Drugs Now" program was piloted reported higher average levels of drug use than did teenagers at private schools in the same counties where the program was not piloted.

D．There is evidence that teenagers who start smoking at an early age are more likely to experiment with illegal drugs than teenagers who do not smoke.

E．The percentage of teenagers who reported using drugs at the schools where the "Stop Drugs Now" program was piloted dropped more in the last year than in any other year over the last decade.

The 150 million people who live outside the country of their birth makeup less than 2.5 percent of world population, but they have an importance far beyond their numbers. Some international migrants are refugees or students, but those with the most impact are economic migrants, drawn to places such as Los Angeles, where the wages may be three times greater than those in Bombay. These migrants tend to be young and willing to work for low wages. Though traditionally unskilled, a growing number are highly educated.

Immigration is now the major contributor to demographic change in many developed countries. In the U.S., according to the latest U.S. Census Bureau projection, the population will grow by 129 million in the period from 2000 to 2050, but if immigration stops it would go up by just 54 million. Western Europe's population is 42 percent greater than that of the U.S., but its projected immigration is only about half that of the U.S.; as a consequence, the region expected to lose 28 million people over the next 50 years. Japan, which has close to zero net migration, is projected to lose 26 million by 2050. (Deaths will start outrunning births in west Europe and Japan around the middle of this decade.)

During file past six years, the U.S. received 7 percent of the world's international migrants, compared with 9 percent by Germany, the second most popular destination. One fourth of all migrants to the U.S. went to California; favorite cities, in order of the number of foreign-born, are Los Angeles, New York City, San Francisco, Miami and Chicago.

International migrants primarily come from developing countries, with China at 14 percent and Mexico at 8 percent being the largest sources. A few developing countries, Afghanistan, Bosnia, Liberia and Rwanda—have had significant influxes in recent years, but these reflect mainly the movement of refugees. Most developing countries had negative net migration.

In the past few years, every European country with considerable immigration has had a reaction against foreign workers, according to social scientist Christopher Jencks of Harvard University. Some Asian countries hit hard by recession in the late 1990s tried to repatriate migrant workers. Thus far the U.S. shows no signs of reinstituting the extremely restrictive immigration laws of the past, a major reason being the dependence of many industries on a supply of foreign labor. Indeed, the AFL-CIO, once an opponent of high immigration quotas, has reversed position and is now attempting to organize immigrant. This change in attitude, among other reasons, leads Jencks to conclude that a substantial reversal of the current liberal policies is unlikely.

Which of the following statements does NOT exactly describe the economic migrants?

A．They tend to be young,

B．Many of them are highly educated.

C．They are willing to work for low wages.

D．They constitute 2.5% of the world population.