1. 有些短语变成被动之后需带to He is often heard to play the guitar. 注意： see sb do hear sb do make sb do, 改成被动语态后必须带to 。 see sb do hear sb do make sb do sb be seen to do sb be heard to do sb be made to do Eg ：We often hear him play the guitar 1.Old people should be taken care of. 2.Not all patients are looked over carefully. 3.Paper is used to write on. 2.动词短语后的介词不能省略: Eg: A talk on Chinese history _ us in our school last week. A. is given B. is given to C. was given D. was given to D3. 有些词没有被动语态，你知道有哪些吗？ 1.
