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, make, 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。