12. 動詞的語態(tài)
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　　語態(tài)有兩種：主動語態(tài)和被動語態(tài)。
　　主語是動作的發(fā)出者為主動語態(tài)；主語是動作的接受者為被動語態(tài)。
　1）若賓語補(bǔ)足語是不帶to 的不定式，變?yōu)楸粍诱Z態(tài)　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(tài)動詞+ be +過去分詞，構(gòu)成被動語態(tài)。
　　 Coal can be used to produce electricity for agriculture and industry.