1 We were made by my mother to clean the room yesterday.
2 I was passed by David a piece of bread .
3 English must be spoken by us in English class.
4 Knives are used by people to cut things.
5 The bikd can't be put here by you .
方法：1 主动句中的宾语变被动句的主语；主动句的动词由主动结构变被动结构,主动句中的主语变被动句中BY 的短语（如果是代词要变宾格）,
2 时态要一致
3 主动句中省略了TO 的不定式变被动结构时TO要还原（如第一道）