12. 动词的语态
 
  语态有两种:主动语态和被动语态。
  主语是动作的发出者为主动语态;主语是动作的接受者为被动语态。
 1)若宾语补足语是不带to 的不定式,变为被动语态 时,该不定式前要加"to"。此类动词为感官动词。
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)情态动词+ be +过去分词,构成被动语态。
   Coal can be used to produce electricity for agriculture and industry.