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共用题干 Please Fasten Your SeatbeltsSevere

免费考试题库2019-12-17  28
问题 共用题干Please Fasten Your Seatbelts
Severe turbulence（湍流）can kill aircraft passengers.Now,in test flights over the Rocky Mountains, NASA（美国航空航天局）engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.
Clear-air turbulence often catches pilots by surprise.Invisible to radar,it is difficult to forecast and can hurl（用力抛出去）passengers about the cabin.In December 1997 , one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.
However,passengers can avoid serious injury by fastening their seatbelts."It is the only antidote（对 策）for this sort of thing,"says Rod Bogue, project manager at NASA's Dryden Flight Research Center in Edwards,California.
The Center's new turbulence detector is based on lidar,or laser-radar.Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air.The technique depends on the Doppler Effect（多普勒效应）.The wavelength of the light shifts according to the speed at which the particles are approaching.In calm air,the speed equals the plane's airspeed.But as the particles swirl（打漩） in rough air,their speed of approach increases or decreases rapidly.The rate of change in speed corresponds to the severity（激烈程度）of the turbulence.
In a series of tests that began last month,a research jet flew repeatedly into、 disturbed air over the mountain ridges（山脉）near Pueblo , Colorado.The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.
Bogue says that he had"a comfortable amount of time"to fasten his seatbelt.The researchers are planning to improve the lidar's range with a more powerful beam.The system could be installed on commercial aircraft in the next few years.
选项 What does"clear-air turbulence"in Paragraph 1 probably mean?A:A not very rough storm.B:Unexpected disturbed air.C:A kind of visible storm.D:A storm over mountain ridges.
答案B
解析根据第二段第三句，再结合上文可知，clear-air turbulence指的是第二段第三段中的“unexpectedrough air"，又由于disturbed与rough意义相近，故选B。 根据二段最后一句可知，1997年12月份的晴空湍流导致1人死亡、100人受伤，可以说是造成了很多伤亡。 根据第四段最后一句可知，晴空湍流的强度与微粒速度的变化有关。 根据第五段最后一句可知，激光雷达探测器能够探测到前方3千米到8千米之间的晴空湍流，并且预测的晴空湍流的强度和持续时间与真实情况相符。这说明激光雷达探测器能成功地预测晴空湍流。 根据最后一段第二句可知，研究人员正计划改善激光雷达探测器，准备使用更强的电脉冲来提升激光雷达探测器的探测范围。
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