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。

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).

youdao

通过另一部车时必须鸣按喇叭。

While passing another vehicle, you must honk your horn.

youdao

通过另一部车时必须鸣按喇叭。

While passing another vehicle, you must honk your horn.

youdao