英语中有主动和被动两种语态.主动语态表示主语是动作的执行者,被动语态表示主语是动作的承受者.只有及物动词才有被动语态.被动语态由“助动词+及物动词的过去分词”构成.被动语态的助动词同样有时态、人称和数的变化.

1.A new computer was bought to me by my father yesterday.

2.The children are looked after very well by Mrs Zhang.

3.He was seen to come into the meeting-room.(这里注意一下：由于see是感官动词,所以改为被动语态后要加to)

4.English is found very useful by us.

5.A lot of trees are planted by him.

后面的“by…”可加可不加,只要句子表示的是被动的意思就可以了.