can这里为什么to do

Question

ask him to do what he can----------US ，will you？（help）
老师说填to help
不解！

Answer 1

看情况：1.I can answer your question.肯定是 can do something.
2.We do what we can to help him.用的是can to do,因为这个 can 后面省略了do,省略的原因是前面有实意动词do.

有这样一道题：
　　Everyone in our class was working hard and doing what we could _________ a good college.
　　A. enter
　　B. to enter
　　C. entering
　　D. entered [hjmAdHolder]
　　【分析】容易误选A.有的同学一看到空格前的情态动词 could 就断定此处应填动词原形 enter.
　　其实,此题正确答案应是B.此句为省略句,即在 could 后省略了动词 do,若把句子补完整应为Everyone in our class was working hard and doing what we could do to enter a good college.即句中的不定式短语(to enter a good college)是用作目的状语的,而不是与情态动词(could)一起构成谓语.请再看类似例句：
　　(1) They did what they could to comfort her. 他们尽量安慰她.
　　(2) They did everything they could to save her life. 他们尽一切力量拯救她的性命.
　　(3) He studies as hard as he could to catch up with his classmates. 他拼命学习以便赶上他的同学.

Answer 2

这里的 help 并非是直接与 can 衔接的.
请先看这句话：ask him to do something to help US, will you?
这句话你应该明白的
然后你把这句话中的 something 换成 what he can
所以说这里的 help 并非是直接与 can 衔接的
这样讲你明白了吗？本回答被提问者采纳