单项选择题

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

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单项选择题

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

单项选择题

Research is under way to （）

A．discover what causes the sonic boom
B．find a means of eliminating the sonic boom
C．produce the sonic boom at low altitudes
D．reduce the sonic boom to tolerable levels