单选题His success is ______ due to luck.

单选题______ he is, he knows a lot of things.

单选题The other day your cousin paid us an unexpected visit.

单选题I had my radio ______, but it has just stopped working again. A. repairing B. to be repaired C. repaired D. being repaired

单选题My old grandfather enjoys living a ______ life in the village. A. calm B. still C. silent D. quiet

单选题Overhead bridges are often found in many cities, especially in places where traffic is heavy and crossing the road is dangerous. The purpose of building these bridges is to enable people to cross roads safely. Overhead bridges are used in very much the same way as zebra crossing. They are more efficient although less convenient because people have to climb up a long flight of steps. This is inconvenient especially to older people. When people use an overhead bridge, they don"t hold up traffic. However, when they cross a busy road using a zebra crossing, traffic is held up. Hence, many overhead bridges have been built to help people and to keep traffic moving smoothly at the same time. For their own safety, people should be encouraged to use them instead of risking their lives by dashing across the road. Old people may find it a little difficult climbing up and down the steps, but it is still much safer than walking crossing the road with all the danger of moving traffic. Overhead bridges serve a very useful purpose. This will prevent unnecessary accidents and loss of life.

单选题The scientists have absolute freedom as to what research they think is best to ______.

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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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