几道英文复合句单选题,

几道英文复合句单选题,
1.【D】- _____ helps others will be helped.
- So,I'm thankful to and try to help ____ has helped us.
A.whoever whomever B.who whoever
C.who whomever D.whoever whoever
2.【D】In the distance there is a hill,_____ stands a white tower.
A,on the top of it B,on the top of there
C,on the top of where D,on the top of which
3.【D】was natural,he married Mary.
A,Which B,That C,This D,As
4.【B】In an open boat,the three men,_____ an engineer,met with a storm on the sea.
A,one of them were B,one of whom was
C,one of them was D,one of whom were