高一英语阅读专项：限时阅读--科普说明
　　An altimeter is an instrument used in an airplane to tell the pilot how high he is flying.
　　The altimeter used in most airplanes is a kind of barometer which measures air pressure. At sea level this pressure is more than 14 pounds on every square inch of the surface. The higher you go into the air, the lower the air pressure is. An altimeter measures this air pressure to show how high the airplane is above the sea level.
　　But the altimeter does not show how high the plane is above the ground. A plane might be flying at a height of 15,000 feet, but it would be only a thousand feet or so above the ground if the land in that area happened to be 14.000 feet above the sea level.
　　The pilot adjusts(调整)his altimeter to the actual sea-level pressure before leaving the airport and he corrects it in flight by new information given to him by radio. He flies high enough to above any mountain he may pass on his course. The barometer altimeter is correct within above 300 feet.
　　Another kind of altimeter, the radio altimeter, makes use of radio reflection. It calculates the height of the flying plane by sending out electrical signals to the surface below and measuring the time required for them to bounce (弹) back. It is correct within 1-5 feet over water, but it is not reliable over uneven(不平的)land. Big planes usually have both kinds of altimeters.
1. The following drawing shows a plane flying over a mountain, which of the heights is given by the barometer altimeter in the plane at the same moment?


2. The barometer altimeter won't work if the plane flies ______ .
A. beyond the atmosphere          B. above very high land
C. over very uneven ground         D. with 1,000 feet of the ground
3. Suppose a plane using a radio altimeter is flying 10,000 meters above a highland which is 4,000 meters above the sea level. What reading will be given by the altimeter?
A.10,000 meters.                B.4,000 meters.
C.14,000 meters.                D.6,000 meters.
4. Suppose a plane using both kinds of altimeters is flying over a mountainous area where the land rises and falls very abruptly(陡峭的). The pilot keeps his plane steady at the same height. Which kind of reading will you get on each of the altimeters?
A. The readings on both altimeters will remain steady.
B. The readings on both altimeters will rise and fall abruptly.
C. The reading on the barometer altimeter will rise and fall abruptly, while that on the radio altimeter will remain steady.
D. The reading on the radio altimeter will rise and fall abruptly, while that on the barometer altimeter will remain steady.

参考答案：C A A D


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