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,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。