8270 He studied hard at school when he was young, __________ contributed a lot to his success.A1947

He studied hard at school when he was young, __________ contributed a lot to his success.A

He studied hard at school when he was young, __________ contributed a lot to his success.

A.which

B.therefore

C.that

D.what

请帮忙给出正确答案和分析，谢谢！