In 1975 Chinese survey teams remeasured Mount Everest, the highest of the Himalayan mountains. Like the Britishin 1852, they used the age-old technique of “carrying in” sea level: surveyorsmarched inland from the coast for thousands of miles, stopping at increments ofas little as a few feet to measure their elevation, and marking each incrementwith two poles. To measure the difference in elevation between poles, surveyorsused an optical level—a telescope on a level base—placed halfway between thepoles. They sighted each pole, reading off measurements that were then used tocalculate the change in elevation over each increment. In sight of the peaksthe used theodolites telescopes for measuring vertical and horizontal angles—todetermine the elevation of the summit.
TheChinese, however, made efforts to correct for the errors that had plagued theBritish. One source of error is refraction, the bending of light beams as they pass through air layers of different temperature andpressure. Because light traveling down from a summit passes through many suchlayers, a surveyor could sight a mirage rather than the peak itself. To reducerefraction errors, the Chinese team carried in sea level to within five totwelve miles of Everest’s summit, decreasing the amount of air that lightpassed through on its way to their theodolites. The Chinese also launchedweather balloons near their theodolites to measure atmospheric temperature andpressure changesto better estimate refraction errors. Another hurdle is thepeak’s shape. When surveyors sight the summit, there is a risk they might notall measure the same point. In 1975 the Chinese installed the first surveybeacon on Everest, a red reflector visible through a theodolite for ten miles,as a reference point. One more source of error is the unevenness of sea level.The British assumed that carrying in sea level would extend an imaginary linefrom 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?
refraction 要求定位到第一个source，One source of error is refraction，其他统统不是和折射有关的！
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.
错了，正确答案是D 这题怎么也想不明白呀~谁来敲我一下头，谢谢唔
------------------------------------------------------------------
Q33: Which of the following best describes the purpose of the sentence in lines 23-25 (“The Chinese…the British”)?
A. Introduce a definition
B. Signal a transition in focus
C. Summarize the preceding paragraph
D. Draw a contrast between two different theories.
E.  resent information that contradicts the preceding paragraph.
Q34: Which of the following is NOT mentioned as a possible source of error in surveying mountain elevation?
A. Mirages
B. Refraction
C. Inaccurate instruments
D. Variations in sea level
E. Uncertainty about the exact point to be measured
---------------------------------------------------------------
Q35: The primary purpose of the passage is to
A. provide details about improvements to a process
B. challenge the assumptions underlying a new method
C. criticize the way in which a failed project was carried out
D. call for new methods to solve an existing problem
E. explain the theory behind a new technique
官方答案是DBCA
-- by 会员 demonada (2010/10/22 21:57:16)
怎么会不明白呀？定位到红色字部分 | 
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2010-10-22 21:57:16
收藏
收藏
楼主