单选题Scientists have devised ways to collect solar energy in one area of a building and carry it to another area. Solar collectors collect and change solar energy into heat energy. These devices are positioned on a building in a 1 that allows for maximum exposure to sunlight. Some can 2 be moved or tilted to follow the sun. Many collectors are flat metal plates painted black. They are painted black because a dark surface absorbs solar energy better than a 3 one. Water or air passing in pipes 4 the plates is heated. The warm water or air is then pumped to places 4 it is needed. The same water or air can be used over and over to absorb and transport heat. Solar cells are used to collect solar energy and 6 it into electric energy. These devices are used on space flights. Large panels covered with thousands of solar cells provide electric power for the spacecraft. On Earth, solar cells are in use in homes and businesses. Buildings using solar cells or solar collectors or 7 exist today. It is probable that more will be built in the future. However, the conversion of already existing buildings to solar energy is not realistic in most 8 due to the 9 involved. Also, most existing buildings are not located or positioned for maximum exposure to sunlight. 10 , the use of solar energy to 11 the energy needs of a single building is growing. What about using solar energy on a large scale to provide electricity, not just for a 12 home, but for a whole 13 ? The problem here is that the sun"s energy, 14 plentiful, is spread out over an enormous area. Suppose solar cells were being used to produce as much electricity as the 15 currently being produced in the United States by other 16 . Experts estimate that this 17 require solar cells covering from 25000 to 70000 square kilometers of land! As the use of solar energy grows and is 18 investigated, more practical and effective applications of it will be developed. Although it does not seem to have a negative effect on the environment, there is a possibility that the widespread use of solar energy might 19 some change in the overall distribution of heat from the sun. However, at the present time, solar energy does appear to be a promising energy alternative. People should also 20 that once they have paid the price for the purchase and installation of solar energy devices, the sunlight is free.

单选题My friend Mr. Black has come to China every year ______ he was a boy.

单选题He ______ TV all afternoon. I can't get him away from it. A. watched B. is watching C. has watched D. has been watching

单选题After the earthquake, the first thing the local government did was to provide ______ for the homeless families.

单选题Jim is very annoyed. Everyone was invited to the evening party ______ him.

单选题I know that you are extremely busy, so I won"t ______ any more of your time.

单选题Jim, like the rest of the students in the class, usually ______ to school on time. A. comes B. come C. are coming D. has come

单选题 When doctors need information about what dose of medicine to prescribe, they usually consult a fat blue book called the Physicians' Desk Reference, or PDR. But the doses recommended in the PDR may be too high for many people and may cause bad reactions, ranging from dizziness (头晕) and nausea(恶心)all the way to death, according to an article published last month in the journal Postgraduate Medicine. For many drugs, smaller doses would work just as well, with far less risk of bad reactions, said the author, Jay Cohen, an associate professor at the University of California. "Side effects drive a lot of people out of treatment that they need," Dr. Cohen said. "People often gave up trying to treat their illnesses when they found that the cure was worse than the disease. But if doctors were to individualize doses for each patient, more people might take their medicine. " Dr. Cohen said he became aware of the problem because he met many patients who suffered from side effects even though they had taken what were supposedly the correct doses of medicine. When Dr. Cohen consulted medical journals and textbooks, he discovered studies showing that many patients were helped by smaller than usual amounts of medicine. And many of his own patients did better with reduced doses. Dosing guidelines generally tend to be too high because they are based on studies conducted with limited numbers of patients by drug companies when they are seeking approval for new products, Dr. Cohen said. For those studies to run efficiently, doses need to be high enough to show as quickly as possible that the drug works. But later, after the drug is approved, far more people take it, sometimes along with other drugs, and individual differences begin to show up. That information does not always make it into the PDR, Dr. Cohen said. Dr. Cohen cautioned that patients should not try to change doses of prescription on their own. He said they needed to work with doctors to adjust the doses safely.

单选题Sunlight can be used to ______ electricity. A. producing B. be producing C. have produced D. produce

单选题Not knowing the language of the country he was visiting, John had a hard time making himself ______.

单选题There are two major problems linked with atomic power plants, ______ the first concerns nuclear waste.

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单选题You should keep the milk in the ice box, ______ it will go bad.

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单选题When it ______ maths, I might as well keep silent.

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单选题Incomes in these countries are very unequally ________ , with a few very rich and many very poor people.

单选题(C) If one takes a sample of the element gold and starts breaking it into smaller and smaller and smaller pieces, it seems reasonable that one will eventually (最终) reach a "smallest possible piece" of gold that could not be divided further and still be called gold. This smallest possible unit of gold would be a gold atom. Thus, the atom is the limit of chemical subdivision for an element. The concept of an atom is an old one, dating back to ancient Greece. Records indicate that around 460 B.C., Democritus, a Greek philosopher, suggested that continued subdivision of matter ultimately would yield small indivisible particles which he called atoms (from the Greek word atomos meaning "uncut or indivisible"). Democritus"s ideas about matter were, however, lost (forgotten) during the Middle Ages, as were the ideas of many other people. It was not until the beginning of the nineteenth century that the concept of the atom was "rediscovered". John Dalton (1776--1844), an English school teacher, proposed in a series of papers published in the period 1803--1807 that the fundamental building block for all kinds of matter was an atom. Dalton"s proposal had as its basis experimentation that he and other scientists had conducted. This is in marked contrast to the early Greek concept of atoms, which was based solely on philosophical speculation (构想). Because of its experimental basis, Dalton"s idea got wide attention and stimulated new work and thought concerning the ultimate building blocks of matter. Additional research, carried out by many scientists, has now validated (证明……有效) Dalton"s basic conclusion that the building blocks for all types of matter are atomic in nature. Some of the details of Dalton"s original proposals have had to be modified in the light of recent more sophisticated experiments, but the basic concept of atoms remains.

单选题By the time students complete that course they know two computer languages and have no trouble ________ their own programs.

单选题When a rare disease ALD threatened to kill the four-year-old boy Lorenzo, his parents refused to give up hope. Doctors explained that there was no cure for ALD, and that he would probably die within three years. But Lorenzo"s parents set out to prove the doctors wrong. The parents devoted themselves to keeping their son alive and searching for a cure. But doctors and the families of other ALD patients often refused to take them seriously. They thought the efforts to find a cure were a waste of time, and drug companies weren"t interested in supporting research into such a rare disease. However, the parents still refused to give up and spent every available hour in medical libraries and talking to anyone who would help. Through trial and error, they finally created a cure from ingredients (调料) commonly found in the kitchen. The cure, named "Lorenzo"s Oil", saved the boys life. Despite the good results, scientists and doctors remained unconvinced. They said there was no real evidence that the oil worked and that the treatment was just a theory. As a result, some families with ALD children were reluctant to try it. Finally, the boy"s father organized an international study to test the oil. After ten years of trials, the answer is: the oil keeps ALD children healthy.