楼上6,9,10有错:
1.More trees must be planted by us.
2.A large hole should be digged by us.
3.When were these books written by Lu Xun?
4.Was the bridge built in 1998 by them?
5.Apples aren't grown by the farmers on the farm.
6.A mouse was seen to run into the room by me.
7.The twins are asked not to swim in the lake by mum.
8.The classroom wasn't cleaned by them yesterday.
9.He is often heard to sing English songs by me.
10.The children were watched to sing that morning by them.
（see/hear/watch sb.do sth.变被动后省略的不定式符号to要补上:sb.be seen/heard/watched to do sth.补充的那个也是被动语态）