中国名校英语四级密卷1.docVIP

中国名校英语四级密卷（1） ension (35 minutes) Directions:There are 4 passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A), B), C) and D). You should decide on the best choice and mark the corresponding letter on the Answer Sheet with a single line through the center.Passage OneQuestions 21 to 25 are based on the following passage.Antarctica has actually become a kind of space station—a unique observation post for detecting important changes in the world’s environment.S1 Remote from major sources of pollution and the complex geological and ecological systems that prevail elsewhere, Antarctica makes possible scientific measurements that are often sharper and easier to interpret than those made in other parts of the world.Growing numbers of scientists therefore see Antarctica as a distantearly warning sensor, where potentially dangerous global trends may be spotted before they show up to the north. One promising field of investigation is glaciology. Scholars from the United States, Switzerland, and France are pursuing seven separate but related projects that reflect their concern for the health of the West Antarctic Ice Sheet—a concern they believe the world at large should share.The Transantarctic Mountain, some of them more than 14,000 feet high, divide the continent into two very different regions. The part of the continent to the “east” of the mountains is a high plateau covered by an ice sheet nearly two miles thick. “West” of the mountain, the half of the continent south of the Americas is also covered by an ice sheet, but there the ice rests on rock that is mostly well below sea level. If the West Antarctic Ice Sheet disappeared, the western part of the continent would be reduced to a sparse cluster of island.While ice and snow are obviously central to many environmental experiments, others focus on the mysterious“dry valley”of Antarctica, valleys that contain little ice