12. 動(dòng)詞的語態(tài)
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　　語態(tài)有兩種：主動(dòng)語態(tài)和被動(dòng)語態(tài)。
　　主語是動(dòng)作的發(fā)出者為主動(dòng)語態(tài)；主語是動(dòng)作的接受者為被動(dòng)語態(tài)。
　1）若賓語補(bǔ)足語是不帶to 的不定式，變?yōu)楸粍?dòng)語態(tài)　時(shí)，該不定式前要加"to"。此類動(dòng)詞為感官動(dòng)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(dòng)詞+ be +過去分詞，構(gòu)成被動(dòng)語態(tài)。
　　 Coal can be used to produce electricity for agriculture and industry.