A
2、 The books must be returned within two months.
3、Children can't be allowed to watch too much TV.
4、The rules may be forgotten when they are playing the match.
5、Must the email about the meeting be sent to you now?
6、A decision should be made before this Friday.
B
2、 has been washed
3、has been broken
4、has been cleaned up
5、has been used
6、have been made
C
2、 have been hidden
3、have been taken
4、has been stolen
5、must be used
6、may be put
7、may be known
8、can be found