what how when where which和in which的用法和区别 指什么时候加to,什么时候不加to

w疑问词后面接动词加to连接,如果更从句就跟句句子用不着To了
用法
1:
i don not know what to do
i don not how to do it
2
i don't know where the girl is
i don't know in which the girl is
(where 主要和in which 荣誉混淆）
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