题目内容：

cannot but cannot help but do nothing but区别
we admire the work they have done to save the environment该用哪个改写?为什么?

优质解答

we (cannot but) admire the work they have done to save the environment
cannot but:不得不,必然,不能不

追问：

为什么不用cannot help but 或者do nothing but ？？？？？