情态动词的主动结构 一般式must /can/ could/may/might/ ought to/ used to/ need do

完成式 must /can/ could/may/might/ ought to/ used to/ need have done 例句

We must take measures to protect our environment.

→Measures must be taken to protect our environment.

You ought to water the flowers twice a day.

→ The flowers ought to be watered twice a day 情态动词的被动结构

一般式must /can/ could/may/might/ ought to/ used to/ need be done

完成式must /can/ could/may/might/ ought to/ used to/ need have been done

C. 不定式的被动语态

形式 例句 be going to

be to

be sure to

be certain to + be +过去分词

be due to

be about to 1. The flowers are to be watered twice a day.

2. The thief is sure to be caught.

3. The book is due to be published next month.

4. The meeting is going to be held this weekend.

D.系表结构与被动结构的区别

被动语态表示动作的被执行或承受；而系表结构表示主语的特点，性质或状态 过去分词由too，very，so， much等修饰 e.g. She was so shocked that she couldn't say a word. 过去分词为表示心理，感情，处所等 e.g. He is lost in thoughts.

The school is located in the center of the city. 过去分词为表示 "必然性，趋势性，意向决心等 e.g. The boy is determined to get the book.

remain ,feel , like, stand, grow, become等+过去分词 e.g. The door remained closed all day.

E. 被动语态的注意点

不定式符号to在被动语态中不可省略 She was seen to pass by the window. 表示状态的动词不能用于被动语态，往往意为"容纳，拥有，适合，缺少"如lack, fit, mean, hold, cost, contain, become, look like, consist of etc. The book costs 10 yuan.

The whole group consists of ten members.

She looks like her mother.

The area once lacked water. 及物动词做不及物用+副词（e.g. easily, badly, well , smoothly）,多用主动表被动,主语往往是人 The pen writes well.

The book sells badly.

The cloth wears long.