改为被动1I saw him go into the classrom.2did he buy you the book you wanted?第一句，

改为被动1I saw him go into the classrom.2did he buy you the book you wanted?第一句，

1. He was seen to to into the classroom.
感官动词，see, watch, hear等+宾语+ 宾补。宾补可以是两种形式，doing ,强调动作正在进行；（to）do, 强调过程，主动语态的时候是省略掉to的不定式，被动语态时，要还原to.追问see后不是接ING形式吗追答不是，see后面可以跟两种形式，你原本的句子当中用的结构是see+sb+do. 就是把to 省略了，所以要加上
假如原来的句子当中是see+sb+doing, 改为被动语态就用doing

He was seen to go into the classsrom. 对
变为被动之后要加to

1. He was seen to go into the classsrom.为正确的。
see/make/let sb do sth 主动不加to,改成被动时，不定式前需加to.
He was seen going into the classroom.这句单独也是正确句子，但不符合本题要求。
2.Was the book you wanted bought(by you)?

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