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为主动语态；主语是动作的接受者为被动语态。
1）若宾语补足语是不带to 的不定式，变为被动语态 时，该不定式前要加"to"。此类动词为感官动词。
feel, hear, help, listen to, look at, mak英语e, observe, see, notice, watch
The teacher made me go out of the classroom.
--> I was made to go out of the classroom (by the teacher).
We saw him play football on the playground.
--> 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。
Coal can be used to produce electricity for agriculture and industry.
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。
They let the strange go.---> The strange was let go.
2） 若let 后宾补较长时，let 通常不用被动语态，而用allow或permit 代替。
The nurse let me go to see my classmate in the hospital.
----> I was allowed / permitted to see my classmate in the hospital.
12.2 短语动词的被动语态
短语动词是一个整体，不可丢掉后面的介词或副词。
This is a photo of the power station that has been set up in my hometown.
My sister will be taken care of by Grandma.
Such a thing has never been heard of before..
12.3 表示"据说"或"相信" 的词组
believe, consider, declare, expect, feel , report, say, see, suppose, think, understand