被動語態用法：
1)當我們不知道動作的執行者是誰，或者沒有必要指出動作的執行者時，需用被動語態。
2)當我們需要強調動作的承受者時，常用被動語態。
3)如果需要說出動作的執行者， 用by引導出動作的執行者。
主動語態變爲被動語態時，其謂語動詞的時態要與原句時態保持一致，其謂語動詞的`數要與新主語保持一致。
主動語態變爲被動語態時有以下幾種情況：
1)主語+謂語動詞+賓語
將主動語態的賓語變爲被動語態的主語。
(主動)We bought a book yesterday.
(被動)The book was bought yesterday.
2)主語+謂語動詞+間接賓語+直接賓語
將主動語態中一個賓語變爲被動語態的主語。多數情況下將間接賓語變爲主語。如果直接賓語變爲主語時，間接賓語前要加介詞to / for.
(主動)He showed me a book yesterday.
(被動)I was showed a book yesterday.
(被動)The book was showed to me yesterday.
3)主語+謂語動詞+複合賓語
含有一個由賓語加賓語補足語構成的複合賓語，變爲被動語態時，將主動語態的賓語變爲被動語態的主語，賓語補足語保留不變，成爲主語補足語。
(主動)I found him a good pupil. (賓語補足語)
(被動)He was found a good pupil. (主語補足語)
4)短語動詞變爲被動語態
有些短語動詞相當於一個及物動詞，其後可以接賓語，因此它們也有被動語態，但短語動詞是不可分割的整體，變爲被動語態時不可去掉其後面的介詞或副詞。
(主動)We should look after the patients very well.
(被動)The patients should be looked after very well by us.
5)賓語從句變爲被動語態
若主動語態中是賓語從句，變爲被動語態時常用it作形式主語，而把真正的主語放在後面。
It‘s said that he passed the exam.
被動語態應注意的幾個特殊問題：
(1)不及物動詞帶介詞和介詞賓語，在變爲被動語態時，仍然要帶上介詞。
(主動)The students in class listen to the teacher carefully.
(被動)The teacher is listened to carefully by the students in class.
(2)當動詞帶有複合賓語時，並且賓補是省去“to”的動詞不定式時，在被動語態中應加上“to”。
(主動)They make do all the work.
(被動)We were made to do all the work.
(主動)We often hear her sing English songs.
(被動)She is often heard to sing English songs.
(主動)I see him walk to school.
(被動)He is seen to walk to school.
