which引导的宾语从句要不要加to？求大神解答，谢谢!

要看这个宾语从句中的which做什么成分。

例如：

He asked me which letter was miscarried.  从句中which letter做主语。

He asked me to which room the letter would be sent.   which room做send to的宾语。因此可改写为：

He asked me which room the letter would be sent to.

I was curious as to which one was to be done.

通过上述例子不难发现，to不是凭空存在的，而是存在句中的动词短语或者介宾短语中。