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    B Under proper conditions, sound waves will be reflected from a hillside or other such obstruction. Sound travels at the speed of about one-fifth of a mile per second. If the hill is eleven hundred feet away, it takes two seconds for the sound to travel to the hill and back. Thus by measuring the time between a sound and its reflection the echo, you can calculate the distance to an obstruction. During World War II the British made a practical use of this role to discover German planes on their way to bomb London long before the enemy was near the object. They used radio waves instead of sound waves, since radio waves can pass through fog and clouds. The outnumbered Royal Air Force (RAF) always seemed to the puzzled Germans to be lying in wait at the right time and never to be surprised. It was radio echoes more than anything else that won the Battle of Britain. Since the radio waves were used to tell the direction in which to send the RAF planes and the distance to send them (their range of flight, in other words) ,the device was called radio directing and ranging, and from the first letters the word radar was formed. 1. Sound waves reflected from a hill can be used to calculate the . A. speed of sound B. time between a sound and its echo C. height of the hill D. distance to the hill 2. The British used radio waves because they . A. were more exact than sound waves B. could not be discovered C. could pass through fog and clouds D. were easier to use than sound waves 3. Practical use of radio waves brought about . A. new machines for planes B. a radio directing and ranging device C. new radio sets for BAF bombers D. a discovering device 4. Radar made the British be able to . A. discover German planes on their way to London B. direct the outnumbered RAF planes effectively C. kill German bomber pilots D. both A and B 5. The author of this passage mainly wanted to tell . A. exactly how radar worked B. why the British used radio waves in their device C. how radar came into being D. how radar helped the British win the Battle of Britain 【查看更多】

     

    题目列表(包括答案和解析)

    　　Under proper conditions, sound waves will be reflected from a hillside or other such obstruction (障碍) ． Sound travels at the rate of about one-fifth of a mile per second． If the hill is eleven hundred feet away, it takes two seconds for the sound to travel to the hill and back． Thus, by measuring the time between a sound and its reflection (the echo) you can estimate (估算) the distance to an obstruction．

    　　During World War II the British made a practical use of this principle to discover German planes on their way to bomb London long before the enemy was near the place． They use radio waves instead of sound waves, since radio waves can go through fog and clouds． The British Royal Air Force always seemed to the puzzled Germans to be lying in wait at the right time and never to be surprised． It was radio echoes more than anything else that won the battle of Britain． And it is from “ radio directing and ranging” that the word “radar (雷达) ”came into being．

    1． Sound wave reflected from a hill can be used to estimate the _______．

    A． height of the hill　　 B． speed and sound

    C． distance to the hill　　D． the intensity (强度)of sound

    2． “echo” is the _________ of sound．

    A． speed　　 B． wave

    C． intensity D． reflection

    3． The estimate is based on the _______ ．

    A． direction of the hill　　B． speed of sound

    C． time between sound and its echo D． both B and C

    4． Radio wave helped the English to __________ ．

    A． discover German planes on their way to London

    B． puzzle German pilots C． know the plan of Germans

    D． know the distance between England and Germany

    5． The writer seems to explain________．

    A． exactly how radar works

    B． why the British use radio waves in their battle

    C． how the word radar came to be．

    D． how radar helped the British win the Battle of Britain

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