the liver can use amino acids to manufacture a variety of important substances.

Hydroponics, the science of growing plants, in water or inert substances, represents one of the most innovative practices in modern agricultural development. Not only does it allow greater of the plant growth process, it permits the production of crops in hostile infertile environments.

The first widely publicized soilless gardening experiments were conducted during the 1930s. W. F. Gericke varied nutrient levels among specimens suspended in a gravel substrate (沙砾基质) to demonstrate remarkable alterations in growth. Among the findings that amazed his fellow horticulturists was the production of tomato plants over 6 meters high.

The original hydroponics gardens merely consisted of plants floating in water. It was later discovered that the roots could survive in a number of media, as long as they were supplied with sufficient moisture, nutrients and oxygen. A variety of materials are used in recent versions including gravel, sand, peat, sawdust, plastics and so on. Indeed, one of the most productive methods involves suspending plants in air with a Styrofoam support and spraying them occasionally with nutrient solution to keep them moist.

Many different kinds of materials are suitable for physically containing plants, yet all of these systems share one trait: the culture solution. This nutrient bath is prepared in a tank by dissolving salts which provide the necessary chemicals for plant metabolism. Constant care must be taken to assure that the sodium chloride(氯化纳)levels in the tank do not reach excessive levels as the plants draw water and minerals out of the solution. The acidity of the tank must also be maintained around 6.0 to 6.5 depending on the specific type of plants being harvested.

Although soilless farming is generally more expensive than utilizing fertile land, there are many advantages that make it an important alternative to traditional practices. Herbicides and pesticides are unnecessary because of the controlled environment. The plants also need less space to grow because their nutrient uptake is significantly more efficient. The most outstanding benefit, though, is the ability to produce crops in areas with poor soil conditions or insufficient rainfall.

Earth is mentioned by the author as a necessity for hydroponics.

A．Right

B．Wrong

C．Not mentioned

This energy comes from substances stored in the cells of the body. These substances ______ energy by combining with oxygen.

A．disperse

B．release

C．develop

D．transmit

Breakfast

1 If you have to miss one meal a day (or if you want to do so), which meal will cause you fewest health problems if you don't eat it? If they have to make a decision of this type, most people (especially dieters or very busy people) will choose to skip breakfast

2 However, many experts in the field of health consider breakfast (the meal which "breaks" your "fast" which started the night before) to be the most important meal of the day. If we eat a good breakfast, they say, we will have the energy and nutrients we need to begin our working day with vigor and hopefully with good humor. Nevertheless, many people skip breakfast or substitute a donut and a cup of coffee for a well-balanced meal What happens if we ignore the importance of breakfast?

3 One recent study conducted in the United States tesled a large number of people Participants included both males and females who ranged in age from 12 to 83. During the experiment, these people were given a variety of breakfast, and sometimes, they had to skip breakfast completely. Special tests, including blood tests and endurance tests, were setup to analyze how well the participants, bodies functioned when they had eaten a certain kind of breakfast.

4 The results showed that if a person eats an adequate breakfast. he or she will work more efficiently and more productively than if he or she skips breakfast or eats a very poor breakfast. This fact appears to be especially true if a persofl,s work involves mental activity The study showed that if schoolchildren eat fruit, eggs, bread, and milk before going to school, they will learn more quickly and will be able to concentrate on their lessons for a longer period of time than if their breakfast diet is inadequate

5 The study also showed that, contrary to what many people believe, if you skip breakfast, you will not lose weight. This is because people become so hungry if they skip breakfast that they eat so much for lunch and end up gaining weight instead of losing. So remember, if you are on a diet, skipping breakfast will not help you. You will probably lose more weight if you reduce your other meals

Questions 21-30 are based on Passage .

21. The word "dieters" means "those who restrict themselves to a special diet in order to control their weight"

22. In the word "breakfast", "fast" probably means "going without food"

23. Many experts in the field of health think that breakfast is most important in a

working day.

24. Some people will substitute a donut and a cup of coffee for a regular breakfast

25. Those participating in the experiment were all adults.

26. During the experiment, these people were given very good breakfast

27. Special tests were set up to analyze how the participants, bodies functioned when they had eaten particular breakfast

28. The results showed that if a efficiently eats a big breakfast, he or she will work

29.The study showed that if schoolchildren have adequate breakfasts before going to school

30. We can safely say skipping breakfast will help one lose weight

Pollutants are substances which, when present at high enough concentrations, produce harmful effects on people and/or the environment.

Sulfur dioxide

Sulfur dioxide is produced when coal and oil are burnt or when minerals are "roasted" to remove the sulfur. In some countries, particularly in the northern hemisphere, coal and oil contain significant amounts of sulfur. Unless special steps are taken to remove sulfur dioxide, it is released into the atmosphere. Power stations and industrial plants, which are often sited close to cities, can produce large quantities of the gas.

As well as affecting human health, sulfur dioxide can be harmful to plants, turning leaves yellow and drying, bleaching, and even killing, foliage.

In the atmosphere, sulfur dioxide can form. acidic particles, or react with cloud droplets, contributing to acid rain.

Particles

Particles in the air come from a number of sources, including motor vehicles, industrial processes and wood burning. Secondary formation of particles(formation from gaseous emissions )can also contribute significantly to particle levels. Some atmospheric particles are from natural sources. These include wind-blown dust, pollen, sea salt, and material from volcanic eruptions.

Fine particles(particles with a diameter of 10 micrometres or less)can be inhaled deeply into the lungs and have been associated with a wide range of adverse respiratory symptoms. Long-and short-term exposure to such particles has been linked with increased deaths from heart and lung disease.

Lead compounds, which are emitted by motor vehicles fuelled with leaded petrol, are cumulative poisons. They slowly build up in the body.

Urban haze

Urban haze is mainly due to fine particles, which cause scattering or absorption of light. Haze is typically brown and limits visibility.

Studies by CSIRO scientists have found that there are several types of particles present in haze in Australian cities: organic carbon compounds, elemental carbon or soot, salt, sulfates, nitrates and dust.

Photochemical smog

Sometimes, under certain meteorological conditions, the combined effects of a number of air pollutants are worse than the individual effects. Photochemical smog, sometimes seen as a whitish haze present over cities during summer, is an example of this. Photochemical smog is formed on still days when the sun shines on air containing volatile organic compounds(VOCs)and oxides of nitrogen. Volatile organic compounds include hydrocarbons, as well as alcohols, aldehydes and ethers. VOCs in the air arise mainly from automotive fuels and industrial solvents. Chemical reactions driven by sunlight and involving VOCs and oxides of nitrogen form. ozone, a gas harmful to humans, animals and plants.

Air quality indoors

Australians on average spend about ninety-five percent of their time indoors and many pollutants occur at higher concentrations indoors than outdoors because of the materials and appliances used in buildings.

Many people's main exposure to air pollutants occurs when they are indoors, such as at home, in the workplace or in entertainment venues.

Researchers are working towards measuring individual exposure to pollutants. That is, a measure of the actual exposure that people have to air pollutants during their daily routines, rather than measures of pollution at fixed locations.

CSIRO regularly uses personal air pollution detectors, which monitor concentrations of pollutants that people breathe. The inexpensive samplers offer scientists, environmentalists, engineers and others a simple but accurate way of measuring selected pollutants in air. The sampler, based on a Swedish

design, is small and requires no electricity so is ideal for remote use. Nitrogen dioxide, sulfur dioxide, ammonia and oth

A．Y

B．N

C．NG

阅读材料，回答题。

How does Organisms Ward off Invaders

The livelihood of each species in the vast and intricate assemblage of living things depends on the existence of other organisms．This interdependence is sometimes subtle，some times obvious．Perhaps the most straightforward dependence of one species on another occurs with parasites，organisms that live on or in other living things and derive nutrients directly from them．The parasitic way of life is widespread．A multitude of microorganisms(including viruses and bacteria，and an army of invertebrates or creatures lacking a spinal column(including crustaceans，insects，and many different types of worms)make their livings directly at the expense of other creatures．In the face of this onslaught，living things have evolved a variety of defense mechanisms for protecting their bodies from invasion by other organisms．

Certain fungi and even some kinds of bacteria create substances known as antibiotics into their external environment．These substances are capable of killing or inhibiting the growth of various kinds of bacteria that also occupy the area，thereby eliminating or reducing the competition for nutrients．The same principle is used in defense against invaders in other groups of organisms．For example，when attacked by disease--causing fungi or bacteria，many kinds of plants produce chemicals that help to ward off the invaders．

Members of the animal kingdom have developed a variety of defense mechanisms for dealing with parasites．Although these mechanisms vary considerably，all major groups of animals are capable of detecting and reacting to the presence of“foreign”cells．In fact，throughout the animal kingdom from sponges to certain types of wornls shellfish，and all vertebrates(creatures possessing spinal column)

there is evidence that transplants of cells or fragments of tissues into an animal are accepted only if they come from genetically compatible or closely related individuals．

The ability to distinguish between“self”and“non-self”，while present in all animals，is most efficient among vertebrates，which have developed an immune system as their defense mechanism．The immune system recognizes and takes action against foreign invaders and transplanted tissues that are treated as foreign cells．

What does the passage mainly discuss? 查看材料

A.How parasites reproduce

B.How organisms react to invaders

C.How antibiotics work to cure disease

D.How the immune system of vertebrates developed