In the lecture, we have mentioned _____ kinds of essay structure of comparison and contrast.

听力原文： Lecturer: In the last lecture, we looked at the adverse effects of desert dust on global climate. Today we're going to examine more closely what causes dust storms and what other effects they can have. As you know, dust storms have always been a feature of desert climates, but what we want to focus on today is the extent to which human activity is causing them. And it is this trend that I want to look at, because it has wide-ranging implications. So, what are these human activities? Well, there are two main types that affect the wind erosion process, and thus the frequency of dust storms. There are activities that break up naturally wind-resistant surfaces such as off-road vehicle use and construction and there are those that remove protective vegetation cover from soils, for example, mainly farming and drainage. In many cases the two effects occur simultaneously which adds to the problem.

Let's look at some real examples and see what I'm talking about. Perhaps the best-known example of agricultural impact on desert dust is the creation of the USA's 'dust bowl' in the 1930s. The dramatic rise in the number of dust storms during the latter part of that decade was the result of farmers' mismanaging their land. In fact, choking dust storms became so commonplace that the decade became known as the 'Dirty Thirties'.

Researchers observed a similar, but more prolonged, increase in dustiness in West Africa between the 1960s and the 1980s when the frequency of the storms rose to 80 a year and the dust was so thick that visibility was reduced to 1,000 metres. This was a hazard to pilots and road users. In places like Arizona, the most dangerous dust clouds are those generated by dry thunderstorms. Here, this type of storm is so common that the problem inspired officials to develop an alert system to warn people of oncoming thunderstorms. When this dust is deposited it causes all sorts of problems for machine operators. It can penetrate the smallest nooks and crannies and play havoc with the way things operate because most of the dust is made up of quartz which is very hard. Another example - the concentration of dust originating from the Sahara has risen steadily since the mid-1960s.

This increase in wind erosion has coincided with a prolonged drought, which has gripped the Sahara's southern fringe. Drought is commonly associated with an increase in dust-raising activity but it's actually caused by low rainfall which results in vegetation dying off.

One of the foremost examples of modern human-induced environmental degradation is the drying up of the Aral Sea in Central Asia. Its ecological demise dates from the 1950s when intensive irrigation began in the then Central Asian republics of the USSR. This produced a dramatic decline in the volume of water entering the sea from its two major tributaries. In 1960, the Aral Sea was the fourth-largest lake in the world, but since that time it has lost two-thirds of its volume, its surface area has halved and its water level has dropped by more than 216 metres. A knock-on effect of this ecological disaster has been the release of significant new sources of wind-blown material, as the water level has dropped.

And the problems don't stop there. The salinity of the lake has increased so that it is now virtually the same as sea water. This means that the material that is blown from the dry bed of the Aral Sea is highly saline. Scientists believe it is adversely affecting crops around the sea because salts are toxic to plants.

This shows that dust storms have numerous consequences beyond their effects on climate, both for the workings of environmental systems and for people living in drylands ...

SECTION 4 Questions 31-40

Questions 31-32

Complete the notes using NO MORE THAN THREE WORDS for each answer

Main focus of lecture: the impact of 【31】______ on the occurrence of dust st

A、five

B、six

C、seven

D、eight

All of us will work in our jobs with different kinds of people and we have to possess certain characteristics to keep on good terms with our co-workers. What do you think is the most important characteristic of a co-worker? Write a composition of about 400 words on the following topic: The Most Important Characteristic of a Co-worker In the first part of your writing you should present your thesis statement, and in the second part you should support the thesis statement with appropriate details. In the last part you should bring what you have written to a natural conclusion or a summary. Marks will be awarded for content, organization, grammar and appro-priacy. Failure to follow the above instructions may result in a loss of marks.

Pain

All of us have felt pain. We have cut ourselves. We have been burned. Or we have had headaches. Some of us suffer pain rarely_______46)

Pain can take complete control of our body and mind, making it impossible to move and even to think. Yet we need pain. Without it, we would not know if we have hurt ourselves. It is our body's warning system________­­­­_47)

Pain is the most common reason we go to a doctor. It is the most common reason we take medicines. Until recently, however, most doctors knew of only a few drugs that stopped some pains_________(48) But new knowledge about the process of pain is helping them to control pain better.

Scientists have learned that the sense of pain is made up of both chemical and electrical signals_________(49) Scientists also have learned that the nervous system sends two different kinds of pain messages to the brain: one very fast, the ether slow.

The first message is the warning signal. It moves at a speed of 30 meters a second. In less than a second, the brain understands that part of the body is hurt and how badly it is injured________(50) It tells us not to use the injured part until it heals.

A．And others have painful attacks all the time.

B．These signals travel from nerve cells in the injured area, up the spinal cord (脊髓) to the brain, and back down again.

C．It tells us that we are injured and should do something about it.

D．They knew little about the process of pain itself.

E．The other message moves at a speed of only one meter a second.

F． And they send the second, slower message of pain to the brain.

第 46 题 请选择（46）处的最佳答案．

With the steady increase in the amount of leisure time that people enjoy today, the importance of businesses that deal with leisure products and services is also steadily increasing.

One of the biggest such industries is the tourist industry. Providing transportation and accommodations for tourists—and guides, brochures, souvenirs—is one of the major industries in many countries.

Another industry obviously devoted to leisure is entertainment. Movies, TV, shows, concerts and plays are usually intended for our leisure. The same can be said of most books, except textbooks.

This list could be greatly extended. But even among these industries, we have mentioned only part of the picture. The people who make TV sets and build the theatres and hotels are as much a part of the leisure industry as the singers or the hotel clerks.

Introduction: Growing【46】.

Some aspects of leisure industry:【47】.

【48】.

Other related industries:【49】.

【50】.

(In) our school library, we (have) (all kinds of) English papers, English Weekly (including).

A．In

B．have

C．all kinds of

D．including

We have to adjust ourselves () all kinds of situations.

A、on

B、to

C、in

D、towards

Exactly where we will stand in the long war against disease by the year 2050 is impossible to say. (111) But if developments in research maintain their current pace, it seems likely that a combination of improved attention to dietary and environmental factors, along with advances in gene therapy and protein-targeted drags, will have virtually eliminated most major classes of disease.

From an economic standpoint, the best news may be that these accomplishments could be accompanied by a drop in health-care costs. (112) Costs may even fall as diseases are brought under control using pinpointed, short term therapies now being developed. By 2050 there will be fewer hospitals, and surgical procedures will be largely restricted to the treatment of accidents and other forms of trauma (外伤). Spending on nonacute (慢性病的) care, both in nursing facilities and in homes, will also fall sharply as more elderly people lead healthy lives until close to death.

One result of medicine's success in controlling disease will be a dramatic increase in life expectancy. (113) The extent of that increase is a highly, speculative matter, but it is worth noting that medical science has already helped to make the very old (currently defined as those over 85 years of age) the fastest growing segment of the population. Between 1960 and 1995, the U. S. population as a whole increased by about 45%, while the segment over 85 years of age grew by almost 300%. (114) There has been a similar explosion in the population of centenarians, with the result that survival to the age of 100 is no longer the newsworthy feat that it was only a few decades ago. U. S. Census Bureau projections already forecast dramatic increase in the number of centenarians in the next 50 years: 4 million in 2050, compared with 37, 000 in 1990.

(115) Although Census Bureau calculations project an increase in average life span of only eight years by the year 2050, some experts believe that the human life span should not begin to encounter any theoretical natural limits before 120 years. With continuing advances in molecular medicine and a growing understanding of the aging process, that limit could rise to 130 years or more.

(81)