请输入或粘贴题目内容
搜题
拍照、语音搜题，请扫码下载APP
题目内容
（请给出正确答案）
A sonic boom is like every sound in that it is ______.
A．explosive
B．caused by compressed tar
C．a pressure disturbance
D．shock wave
答案
更多“A sonic boom is like every sound in that it is ______.A．explosiveB．caused by compressed ta”相关的问题
第1题
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
第2题
An appropriate title for this passage would be ______.
A．The Sonic Boom
B．Air and Its Effects
C．Faster Than Sound
D．Problems Facing Aviation Today
第4题
Questions 21 to 25 are based on the following passage.
There is a difference between science and technology. Science is a method of answering theoretical questions; technology is a method of solving practical problems. Science has to do with discovering the facts and relationships between observable phenomena in nature and with establishing theories that serve to organize these facts and relationships; technology has to do with tools, techniques, and procedures for implementing the finding of science.
Another distinction between science and technology has to do with the progress in each.
Progress in science excludes the human factor. Scientists, who seek to comprehend the universe and know the truth within the highest degree of accuracy and certainty, cannot pay attention to their own or other people's likes or dislikes or to popular ideas about the fitness of things. What scientists discover may shock or anger people-as did Darwin's theory of evolution. But even an unpleasant truth is more than likely to be useful; besides, we have the choice of refusing to believe it! But hardly so with technology; we do not have the choice of refusing to hear the sonic boom produced by a supersonic aircraft flying overhead; we do not have the option of refusing to breathe polluted air; and we do not have the option of living in a non-atomic age. Unlike science progress, technology must be measured in terms of the human factor. The legitimate purpose of technology is to serve people in general, not merely some people; and future generations, not merely those who presently wish to gain advantage for themselves. Technology must be humanistic if it is to lead to a better world.
21. The difference between science and technology lies in that _____.
A) the former provides answers to theoretical questions while the latter to practical problems
B) the former seeks to comprehend the universe while the latter helps change the material world
C) the former aims to discover the inter-connections of facts and the rules that explain them while the latter, to discover new designs and ways of making the things we use in our daily life
D) all of the above
22. Which of the following may be representative of science？
A) The improvement of people's life.
B) The theory of people's life.
C) Farming tools.
D) Mass production.
23. According to the author, scientific theories _____.
A) must be strictly objective
B) usually take into consideration people's likes and dislikes
C) should conform. to popular opinions
D) always appear in perfect and finished forms
24. The author states that technology itself _____.
A) is responsible for widespread pollution and resource exhaustion
B) should serve those who wish to gain advantage for themselves
C) will lead to a better world if put to wise use
D) will inevitably be for bad purpose
25. The tone of the author in this passage is _____.
A) positive
B) negative
C) factual
D) critical
第5题
A.HOV R SUMMIT
B.HOV R VELOC IT I 3
C.HOV R SONIC 3
D.HOV R STRT
第6题
Although residential real estate activity makes up less than 8% of total U.S. GDP, a housing market like this one can make the difference between positive and negative growth. Most significantly, consumer spending is 66% of GDP, and the purchase of a new home tends to have an "umbrella effect" on the homeowner's spending as he has to stock it with a washer/ dryer, a new big-screen TV, and maybe a swing set for the yard.
The main factor in housing's continued strength is a classic economic example of zero-sum boom: the persistent weakness everywhere else. As the 2003 recovery continues to be more forecast than reality. Falling stock prices raised investor appeal for U.S. Treasury Bonds, which in turn, allowed most interest rates to drift even lower. But there are not many signs that there's a bubble ready to burst.
December's new record in housing starts, for example, was nicely matched by the new record in new home sales. If you build it, they will buy and even if an economic pickup starts to reduce housing's relative attractiveness, there's no reason why modest economic growth and improved consumer mood can't help sustaining housing's strength. "The momentum gained from low mortgage interest rates will carry strong home sales into 2003, with an improving economy offsetting modestly higher mortgage interest rates as the year progresses", said David Lereah, chief economist at the National Association of Realtors.
Just as housing has taken up much of the economic slack for the past two years, both as a comforting investment for fretting consumers and a driver of consumer spending itself, a big bump elsewhere in the economy in 2003 could be housing's downfall. If stocks roar back this spring, capital inflows could steal from the bond market, pushing up long-term interest rates. Or Alan Greenspan and the Fed could do the same to short-term rates, as a way to hit the brakes on a recovery that is heating up too fast. In other words, if everything possible goes wrong for housing, homeowners should have plenty to compensate them in terms of job security and income hikes.
The author draws a sharp contrast between the housing market and the rest of the economy so as to show
A．the boom of real estate activity.
B．the statistics on home prices.
C．the role of housing market.
D．the degree of consumer spirits.
第7题
【C1】
A．taken
B．pieced
C．kept
D．made
第9题
With a given load on the cargo hook，the thrust on a cargo boom ______.
A.increases as the angle to the horizontal increases
B.increases as the angle to the horizontal decreases
C.is greatest at an angle of 45° and decreases as the boom is raised or lowered
D.is least at an angle of 45° and increases as the boom is raised or lowered
