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.