英语阅读理解 急Under proper conditions,sound waves will be reflected from a hillside or other such obstruction.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 t

英语阅读理解 急Under proper conditions,sound waves will be reflected from a hillside or other such obstruction.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 t
英语阅读理解 急
Under proper conditions,sound waves will be reflected from a hillside
or other such obstruction.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 timing the
interval between a sound and its reflection (the echo),you can estimate the
distance to an obstruction.
During World War II,the British used a practical application of this
principle to detect German planes on their way to bomb London long before
the enemy was near the target.They used radio waves instead of sound
waves,since radio waves can go 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 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 ranges of flight,in
other words),t he device was called radio detecting and ranging,and from
the first letter the word radar was coined.
6.Sound waves reflected from a hill can be used to estimate the _______.
A) intensity of sound B) distance to the hill
C) speed of sound D) height of the hill
7.During World War Two,the British used _______ to detect German
planes.
A) a radio detecting and ranging device B) an electronic sound wave device
C) new electronic instruments for planes D) new radio sets for RAF
8.Radar enabled the English to ________.
A) confuse German bomber pilots B) detect the outnumbered RAF planes effectively
C) detect German planes on their way to London D) both A and B
9.Why did the British use radio waves
A) Because they were more exact than sound waves.
B) Because they could not be detected.
C) Because they were easier to use than sound waves.
D) Because they could go through fog and clouds.
10.What can you conclude from the passage
A) Radar was a practical application of a well-known principle.
B) Light waves could be used in a device similar to radar.
C) Radar greatly increased the effectiveness of the RAF.
D) Sound waves are reflected from a hillside under all conditions.

英语阅读理解 急Under proper conditions,sound waves will be reflected from a hillside or other such obstruction.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 t
6.B) distance to the hill
7.A) a radio detecting and ranging device
8.C) detect German planes on their way to London
9.D) Because they could go through fog and clouds.
10.A) Radar was a practical application of a well-known principle.