where which that引导的定语从句有何区别?

This is the office (where) he worked.(he worked结构完整,不用加宾语）
This is the office (which) he worked in.(he worked in少了个宾语,所以用which或者that都可以）
where引导的定语从句结构完整,不缺主语或宾语；
而which或that引导的定语从句结构不完整,缺主语或宾语.
如：
This is the place that/which we lived in last summer.
That is the school that/which we visited in 2005.I don't know if he will come. (come)这个if是是否的意思，引导宾语从句，从句的结构完整，但意思上应该是“他是否会来”，这if是个连词，也可以换成whetherif he _comes_(come) I'll tell you.这个if是如果的意思，引导的是条件状语从句。条件、时间状语从句中的时态比较特别，用一般现在时表示将来，所以用comes.