12. 动词的语态
语态有两种：主动语态和被动语态。主语是动作的发出者时为主动语态；主语是动作的接受者时为被动语态。
注意：1）感官动词主动语态的宾语补足语是不带to 的不定式，变为被动语态时，该不定式前要加\"to\"。例如：
The teacher made me go out of the classroom. 老师逼我走出教室。
--> I was made to go out of the classroom （by the teacher）.
We saw him play football on the playground. 我们看见他在草场踢球。
--> He was seen to play football on the playground.
2）情态动词+ be +过去分词，构成被动语态。例如：
Coal can be used to produce electricity for agriculture and industry. 煤可以产生工农业需要的电。
12.1 let 的用法
1）当let后只有一个单音节动词，变被动语态时，可用不带to 的不定式。例如：
They let the strange go.他们放陌生人走了。
---> The strange was let go.
