Gwd –26-Q32 to 35----中国人改进了英国人测量珠峰高度的方法 In 1975 Chinese survey teams remeasured Mount Everest, the highest of the Himalayan mountains. Like the British in 1852, they used the age-old (5) technique of “carrying in” sea level: surveyors marched inland from the coast for thousands of miles, stopping at increments of as little as a few feet to measure their elevation, and mark- (10) ing each increment with two poles. To measure the difference in elevation between poles, surveyors used an optical level—a telescope on a level base—placed halfway between the (15) poles. They sighted each pole, read- ing off measurements that were then used to calculate the change in eleva- tion over each increment. In sight of the peaks the used theodolites— (20) telescopes for measuring vertical and horizontal angles—to determine the elevation of the summit. The Chinese, however, made efforts to correct for the errors that (25) had plagued the British. One source of error is refraction, the bending of light beams as they pass through air layers of different temperature and pressure. Because light traveling. (30) down from a summit passes through many such layers, a surveyor could sight a mirage rather than the peak itself. To reduce refraction errors, the Chinese team carried in sea level to (35) within five to twelve mile of Everest’s summit, decreasing the amount of air that light passed through on its way to their theodolites. The Chinese also launched weather balloons near their (40) theodolites to measure atmospheric temperature and pressure changes to better estimate refraction errors. Another hurdle is the peak’s shape. When surveyors sight the summit. (45) there is a risk they might not all measure the same point. In 1975 the Chinese installed the first survey beacon on Everest, a red reflector visible through a theodolite for ten (50) miles, as a reference point. One more source of error is the uneven- ness of sea level. The British assumed that carrying in sea level would extend an imaginary line from (55) the shore along Earth’s curve to a point beneath the Himalaya. In reality, sea level varies according to the irregular interior of the planet. The Chinese used a gravity meter to correct for local deviations in sea level. Q32 It can be inferred from the passage that refraction would be most likely to cause errors in measurements of a mountain’s elevation under which of the following conditions? Answer : D A. When there are local variations in sea level B. When light passes through humid air C. When theodolites are used relatively far from the mountain peak. D. When weather balloons indicate low air temperature and pressure. E. When sea level has been carried in to Within five to twelve miles of the summit. 我觉得答案应该是C 。theodolites离the mountain peak越远,光经过的空气越多,测量越不准确(To reduce refraction errors, the Chinese team carried in sea level to within five to twelve mile of Everest’s summit, decreasing the amount of air that light passed through on its way to their theodolites.)而d中low air temperature and pressure好象没什么意义。恳请大家指点迷津 ,本题困惑挺久了,谢谢大家 |