we should do everything we can to protect the env ironment.句中everything we can 能用什么替代

题目

we should do everything we can to protect the env ironment.句中everything we can 能用什么替代
遇到这样一道选择题,我主观认为what we can 与what we can do 都可,前者更简练.但答案是后者,为什么?恳请高人指点.

答案

we should do everything ( we can)to protect the environment.
我问所能做的一切,要体现出“做”
what we can没动词是不可以的.