4.In big cities you always hear sirens all the time.
在大城市里, 你总能听到。
5.The cars had stopped at the sound of the approaching siren.
这些汽车听到愈来愈近的便停了下来。
6.When he heard the police sirens, he ran off as fast as his legs could carry him.
听到响起,他拚命地跑。
7.The sirens are also found on mirror stands for women to remind them that their beauty and powers of irresistibility are of voice and words as well as appearance.