把主动语态改为被动语态,可以遵循以下几个步骤：
1.把宾语变成被动语态中的主语；
2.找出谓语动词,变成相应的被动.如：一般式变成be done.过去式变成was/were done；
3.把主语变成介词by 的宾语；
4.注意人称、时态和数的变化.
例：1.Bruce writes a letter every week.→A letter is written by Bruce every week.
2.Li Lei mended the broken bike this morning.→The broken bike was mended by Li Lei this morning.
3.He has written two novels so far.→Two novels have been written by him so far.
4.They will plant ten trees tomorrow.→Ten trees will be planted by them tomorrow.
5.Lucy is writing a letter now.→A letter is being written by Lucy now.
6.You must lock the door when you leave.→the door must be locked when you leave.