There is nothing for us____

There is nothing for us____
A.worry about
B.worrying
C.to worry
D.to worry about
2.Some children are arguing about what TV programmes___
A.watching
B.for watching
C.to watch
D.will watch
3.I have____work to do that I can't go out with you.
A.much too B.too much C.so many D.so much
这几题选什么呢,为什么?
我知道答案是D C D,但为什么？