Some of us ( )is very imortant.A(know) B(knows) C(knowing)D(to know)

问题描述:

Some of us ( )is very imortant.A(know) B(knows) C(knowing)D(to know)
是C还是D,还麻烦告诉小弟当两个动词一起出现时,什么时候用Ving形式,什么时候用TO+ V原.

knowing
该句子可以改为() is very important
just like swimming is my faviourt sport