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[主观题]
Sound waves travel in the air in much the same way _____ water waves spread on the w
ater.
A. as
B. that
C. where
D. in which
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题目内容
（请给出正确答案）
ater.
A. as
B. that
C. where
D. in which
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更多“Sound waves travel in the air …”相关的问题
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 penetrate fog and clouds. The outnumbered Royal Air Force(RAF) always seemed to the puzzled Germans to by 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 rage of flight, in other words) , the device was called "radio directing and ranging" , and from the initials the word "radar" was coined.
Sound waves reflected from a hill can be used to estimate the______.
A．height of the hill
B．speed of sound
C．distance to the hill
D．intensity of sound
According to the text, which of the following is true？
A．To put together a trip using a traditional travel agent is not hard at present.
B．To sound the death knell for tour operator is unacceptable and inhumane.
C．Some high-street travel agents defy the model of surviving with the internet.
D．Traditional tour firms grapple with the internet.
A sound is a pressure disturbance: a sonic boom, like other explosive sounds, is the result of an abrupt change in pressure. An airplane in subsonic flight produces weak changed in pressure, but because these disturbances travel at the speed of sound, they move faster than the airplane and stay in front of it. In effect, these disturbances warn the air to get out of the way, and the an does just jet, however, gets ahead of its own pressure disturbances. Consequently a wave of suddenly com pressed air--a shock wave--builds up and is thrown off like the wave ;hat spreads from the bow of a speedboat.
Can sonic booms be eliminated？ The answer is a categorical negative--they are an innerent(内在的) part of supersonic flight--but the sonic boom probably can be reduced; government and private research is now under way to improve understanding of the sonic boom. If and when the booms can be reduced to tolerable levels, commercial supersonic transports can come rata service.
Before commercial airliners travel faster than sound, problems must 0e solved regarding ______.
A．design
B．Construction
C．operation
D．all of the above
(83) Heat waves, rising from the earth, meet resistance in the atmosphere from the water vapor there. Many if the waves are stopped by the water vapor can not get back out into space. The atmosphere, when it is warmed up, also adds some heat back to the earth's surface.
When the sun's rays strike water surface, some of the water becomes absorbed by the air as water vapor. The warmer the air is, the more vapor it can hold. When the air has absorbed its maximum amount of vapor, it is said to be saturated. If the air is then cooled, some of the vapor will condense and clouds will form. (84)These clouds, will contain drops of water at temperatures above freezing, or ice crystals at temperatures below freezing.
Clouds can greatly affect the temperature of the earth's surface. When there are many clouds in the sky, all of the sun's rays can not reach the earth. The cloudy day, then, will be cooler than the cloudless day. Clouds also prevent the earth from cooling off rapidly at night. For this reason, countries such as the British Isles, which are often covered by clouds, have a relatively constant temperature. The weather in these cloudy areas is neither very hot in summer nor very cold in winter. On the other hand, places such as deserts, which have few or no clouds, have very sharp variations in temperature—between night and day as well as between summer and winter.
Radio stations that transmit programs to distant countries send out waves that resemble______.
A．heat waves rising from the earth
B．waves absorbed by water vapor
C．waves sent out by radio stations that transmit local programs
D．the rays sent out from the sun
A.extended
B.nasalized
C.glorified
D.increased
—I'm thinking about Mexico City.
—________.
A.I'm going to see a travel agent tomorrow.
B.That's O.K. I've been busy lately,too.
C.You are？ I love it too. It's a really exciting place.
A.I did nothing but stayed at home
B.I'll visit a friend of mine
C.I'm a tour guide in a travel agency
一 You sound kind of depressed. Is there anything wrong？
一 _____________________
A. I hadn't heard anything from my sister in two weeks.
B. I'm going to Hawail to a holiday.
C. You know what they say,"no news is good news."
A.What
B.Which
C.How
D.Whatever
The model has shown that this radar system, known as laser-doppler radar, can measure with absolute precision speeds varying from spaceship orbital injection (进入) velocities (速度) of five miles per second down to virtual stops--speeds of less than one ten thousandth of an inch per second. According to the scientists who are developing this system, such fine measures of velocity are of prime importance in space missions. In a rendezvous (对接) between two spaceships, or in a landing approach by a vehicle onto an orbiting space station, a bump could rip open a ship's skin, or a nudge could knock the station out of its orbit.
The light-beam radar, which operates at a frequency of trillions (百万兆) of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station. A control system using so precise a signal as this would allow a huge vehicle to dock at a space station as lightly as a feather.
Laser-doppler radar ______. ()
A．measures the movements of a spaceship by means of light beam
B．makes use of microwaves
C．makes use of sound waves
D．Both A and B
