把下列句子改爲被動語態 I often hear Mary sing English songs at home.2.A

題目：

把下列句子改爲被動語態 I often hear Mary sing English songs at home.2.A policeman is running after a theif in the street.

解答：

1.Mary is often heard sing English songs at home(by me).
2.A theif is being run after by a policeman in the street.