語態有兩種：主動語態和被動語態。
主語是動作的發出者爲主動語態;主語是動作的接受者爲被動語態。
1)若賓語補足語是不帶to 的不定式，變爲被動語態 時，該不定式前要加"to"。此類動詞爲感官動詞。
feel, hear, help, listen to, look at, mak英語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。