語態有兩種：主動語態和被動語態。

主語是動作的發出者為主動語態;主語是動作的接受者為被動語態。

1)若賓語補足語是不帶to 的不定式，變為被動語態　時，該不定式前要加"to"。此類動詞為感官動詞。

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)情態動詞+ be +過去分詞，構成被動語態。

Coal can be used to produce electricity for agriculture and industry.