If you want to be healthy,()is().

问题描述:

If you want to be healthy,()is().
A.do more exercise;helping
B.do more exercise;helpful
C.doing more exercise;helpful
D.doing more exercise;helping

C选项应该是正确的
doing more exercise 是动名词,作为后面一句的主语
helpful是形容词,接在Be 动词之后.