1.The teacher finds teaching little Tom （ ）because he is too

1.The teacher finds teaching little Tom （ ）because he is too young.
A.frustrating B.frustrated C.frustrate
2.can you tell me ( )learn a foreign language well.
A.what to B.how to C.how can I
3.mother told her son ( )play too much.
A.to not B.not to C.don't to
4.in the past 后面跟什么形式的动词?