单选题My eyes had become _________ to the now semi-darkness, so I could pick out shapes about seventy-five yards away.

单选题The small group of onlookers presented a Upathetic/U sight and did nothing to help the drowning child.

单选题He couldn't explain the problem well, as he had only a(n) ______ knowledge of the subiect.

单选题The authorities had failed to react fast enough to popular discontent but told citizens that only hard work could bring an improvement in living standards.

单选题The politician says he will the welfare of the people.

单选题Her friends helped her ______ after her sister was killed in a car crash.

单选题There are strict laws about exporting______ animals. A. alive B. living C. lively D. live

单选题Two substitutes were used during the basketball games. A. players B. centers C. referees D. replacements

单选题Eight times within the past million years, something in the Earth"s climatic equation has changed, allowing snow in the mountains and the northern latitudes to accumulate from one season to the next instead of melting away. Each time, the enormous ice sheets resulting from this continual buildup lasted tens of thousands of years until the end of each particular glacial cycle brought a warmer climate. Scientists speculated that these glacial cycles were ultimately driven by astronomical factor: slow, cyclic changes in the eccentricity of the Earth"s orbit and in the tilt and orientation of its spin axis. But up until around 30 years ago, the lack of an independent record of ice-age timing made the hypothesis untestable. Then in the early 1950"s Emiliani produced the first complete record of the waxings and wanings of first glaciations. It came from a seemingly odd place, the seafloor. Single-cell marine organisms called "foraminifera" house themselves in shells made from calcium carbonate. When the foraminifera die, sink to the bottom, and become part of seafloor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabited. In particular, the ratio of a heavy isotope of oxygen (oxygen-18) to ordinary oxygen (oxygen-16) in the carbonate preserves the ratio of the two oxygens in water molecules. It is now understood that the ratio of oxygen isotopes reflects the proportion of the world"s water locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation slightly sooner than molecules containing the lighter isotope. Hence, as water vapor evaporated from warm oceans moves away from its source, its oxygen- 18 returns more quickly to the oceans than does its oxygen-16. What falls as snow on distant ice sheets and mountain glaciers is relatively depleted of oxygen-18. As the oxygen-18-poor ice builds up, the oceans become relatively enriched in the isotope. The larger the ice sheets grow, the higher the proportion of oxygen-18 becomes in seawater--and hence in the sediments Analyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the Earth"s astronomical cycles. Since that pioneering observation, oxygenisotope measurements have been made on hundreds of cores. The combined record enables scientists to show that the re-cord contains the very periodicities as the orbital processes. Over the past 800, 000 years, the global ice volume peaked every 100,000 years, matching the period of the orbital eccentricity variation. In addition, "wrinkles" superposed on each cycle--small decreases or surges in ice volume--have come at intervals of roughly 23,000 and 41,000 years, in keeping with the precession and tilt frequencies of the Earth"s spin axis.

单选题What the passage tells us can be summarized by the statement ______.

单选题The source, who spoke on condition of anonymity,______to discuss the implication of that conclusion.(2005年中国科学院考博试题)

单选题Some problems can be readily identified simply by looking around. These problems concern the pollution of our environment by technology as a result of sudden upsets in the physical, economic and social balance. The most obvious of these are the general pollution of our physical environment and the destruction of irreplaceable natural resources. Not so obvious as these, but just as painfully significant to some, are the disappearing and changing of jobs which overnight often create large groups of jobless citizens. Can technology be used to undo what it has done, replace what it has destroyed or substitute for what it has caused to disappear? No one knows. Many wonder whether or not all of the sources of pollution have yet been identified, whether or not they are being arrested and whether or not they will be prevented from recurring. Another set of problems relates to what technological advancement has done to the quality of life. An improved social life has not been unfortunately, either the goal or the chief beneficiary of technological change. Rather, any improvements that have occurred have been more accidental than intended. Too much has happened too fast. The changes demanded of marriage and family relationships remain largely unexamined. It is often a matter of "put up or shut up", and a person has to adapt his life-style to ever-changing conditions with little time for choice. The "no-move-no-advancement" type is an example of one such problem. Many people are coming to think that the reward is simply not worthy the struggle, and they are taking jobs with less responsibility and lower pay.

单选题One billion people in the world are short of water. How can this problem be solved? Some suggestions have been to desalinate (除去盐分) ocean water or to build enormous water pipelines from areas where water is abundant. Suggestions such as these prove extremely costly when they are actually used. One possibility that scientists are considering is pulling icebergs from either the North Pole or the South Pole to parts of the world with a water shortage. Although many questions must be answered before such a project could be tried, moving icebergs seems a reasonable possibility in the future. Engineers, mathematicians, and glaciologists (冰川学家) from a dozen countries have been considering the iceberg as a future source of water. Saudi Arabia is particularly interested in this project because it has a great water shortage. Scientists estimate that it would take 128 days to transport a large iceberg (about 1/2 miles square) to Saudi Arabia. Yet the iceberg would be completely melted by the 104 th day. Therefore, insulation would be essential, but how to insulate the iceberg remains an unsolved problem. The problems in transporting an iceberg are numerous. The first problem is choosing the iceberg to pull. The icebergs that form in the North Pole are quite difficult to handle because of their shape. Only a small portion extends above the water—most of the iceberg is below the surface, which would make it difficult to pull. South Pole icebergs, on the other hand, are flat and float like table tops; thus, they would be much easier, to move. How can a 200 million-ton iceberg be moved? No ship is strong enough to pull such enormous weight through the water. Perhaps several ships could be used. Attaching ropes to an iceberg this size is also an enormous problem. Engineers think that large nails or long metal rods could be driven into the ice. What would happen if the iceberg split into several pieces during the pulling? Even if an iceberg with very few cracks were chosen, how could it be pulled through stormy waters? Furthermore, once the iceberg reached its destination, very few ports would be deep enough to store it. All of these problems must be solved before icebergs can become a reasonable source of water. Yet scientists estimate that it will be possible to transport them in the near future. Each year, enough icebergs form to supply the whole world with fresh water for a full year. In addition, icebergs are free and nonpolluting. As a solution to the world"s water problems, icebergs may be a workable possibility.

单选题Although she was still ill, she ______ herself from the hospital. A. extracted B. discharged C. injected D. drained

单选题Prof. White, my respected tutor, frequently reminds me to ______ myself of every chance to improve my English.

单选题Every living thing has an inner biological clock that controls behavior. The clock works all the time even when there are no outside signs to mark the passing of time. The biological clock tells plants when to form flowers and when the flowers should open. It tells insects when to leave the protective cocoon and fly away. And it tells animals when to eat, sleep and wake. It controls body temperature, the release of some hormones and even dreams. These natural daily events are circadian rhythms. Man has known about them for thousands of years. But the first scientific observation of circadian rhythms was not made until 1729. In that year French astronomer, Jean-Jacques d'Ortous de Mairan, noted that one of his plants opened its leaves at the same time every morning, and closed them at the same time every night. The plant did this even when he kept it in a dark place all the time. Later scientists wondered about circadian rhythms in humans. They learned that man's biological clock actually keeps time with a day of a little less than 25 hours instead of the 24 hours on a man-made clock. About four years ago an American doctor, Eliot Weitzman, established a laboratory to study how our biological clock works. The people in his experiments are shut off from the outside world. They are free to listen to and live by their circadian rhythms. Dr. Weitzman hopes his research will lead to effective treatments for common sleep problems and sleep disorders caused by aging and mental illness. The laboratory is in the Monteflore Hospital in New York City. It has two living areas with three small rooms in each. The windows are covered, so no sunlight or moonlight comes in. There are no radios or television receivers. There is a control room between the living areas. It contains computers, one-way cameras and other electronic devices for observing the person in the living area. The instruments measure heartbeat, body temperature, hormones in the blood, other substances in the urine and brain waves during sleep. A doctor or medical technician is on duty in the control room 24 hours a day during an experiment They do not work the same time each day and are not permitted to wear watches, so the person in the laboratory has no idea what time it is. In the first four years of research, Dr Weitzman and his assistant have observed 16 men between the ages of 21 and 80. The men remained in the laboratory for as long as six months. Last month, a science reporter for The New York Times newspaper, Dava Sobol, became the first woman to take part in the experiment. She entered the laboratory on June 13th and stayed for 25 days. Miss Sobol wrote reports about the experiment during that time, which were published in the newspaper.

单选题Many feel Kennedy"s commitment was a desperate political maneuver to lift himself out of the calamity of the Bay of Pigs.

单选题Mail service will be temporarily ______ because of the strike of the postal workers.

单选题The weather wasn't favorable and both teams had to ______ icy rain and a strong wind during the match. A. pin down B. get stuck in C. take control of D. contend with