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.http://yingyu.chazidian.com --> 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.