there's nothing for them to do but ____ silence.

问题描述:

there's nothing for them to do but ____ silence.
请问这空是填to remain 还是remain,各个感觉应该是填remain,因为前面有实义动词的do,后面不是应该省略to吗,但是答案是to remain.
There is nothing left to him but to hit back.此句我能理解
试比较:There is nothing left for him to do but hit back.而此句跟各位给出的there's nothing for them to do but to remain,到底应该用哪个呢?

but 前面是to do,but后面要跟前面的一致,所以也应该是to do sth