Fire siren! Fire siren! Please evacuate thru nearest emergency exit. Do not use elevator. .
火警！火警！请从就近安全通道撤离，不要使用电梯。
Another example is the word siren, familiar to us as the mechanical device that makes such an alarming sound when police cars, ambulances, or fire engines approach.
另一个例子是“警报器”这个词，是我们很熟悉的一个机械装置，当警车、救护车或消防车靠近时，警报器会发出警报。
It is caused by the Doppler effect (something similar happens when a police car or fire engine with its siren blaring drives past you, and the pitch of the sound suddenly drops).
这是由多普勒效应(类似一辆警车或消防车鸣着警笛从你身边经过，之后音高突然下降)引起的。
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