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更多“sound的含义（）”相关的问题
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
A.试验制动机开始减压时
B.调车作业中，表示已接受调车长所发出的信号
C.接到试验制动机结束的手信号，回答试风人员时
D.发出紧急停车信号时
A.建立一套内容科学、程序严密、配套完备、运行有效的国有企业党的建设制度体系
B.建立一套内容科学、程序严密、运行有效的国有企业党的建设制度体系
C.建立一套内容科学、配套完备、运行有效的国有企业党的建设制度体系
D.建立一套程序严密、配套完备、运行有效的国有企业党的建设制度体系
