that在定语从句中可充当什么成分
定语从句中先行词是those用THAT还是which引导？
定语从句中先行词是those用THAT还是which引导？
先行词为“those＋表事物的复数名词”时， 关系代词通常只用which而不用that。
如：You should grasp well those skills which may be used in the future work.
最后，记得这个特殊情况吧：当先行词是表示原因或方式的名词时，可以用that引导定语从句，相当于介词 which，that可以省略。
如： She likes the child for the very reason that (for which) she loves his father. 她喜欢那个孩子因为她爱着孩子的父亲。
He didnt like the way that (in which) she speaks to his mother. 他不喜欢她对他的母亲那样说话。
Imagine the speed that (at which) he drives the car. 很难想象，他开车开得那么快。
The reason (that /for which /why) he came here was to ask for our help.他来这里的原因是寻求我们的帮助。
同位语从句中that可以做哪些成分？
同位语从句的that不做句子成分，只起连接作用！
英语的同位语从句是名词性从句的一种，名词性从句的引导词可以分为三类：
一. that 无义 不做句子成分
there is no doubt that he will be on time
二. whether /if 意义是 是否 也不做句子成分
whether he will come or not is still unknown
三 各种疑问代词 疑问副词
他们都做句子成分 意义不同
例如： what happened to the dog remained a mystery
that在定语从句里可以做主语吗？
可以的 It is the knife that made you out of trouble.Whether that is possible does not have any needs to be judged by the manager.I think that is a good problem is what that question whether that is a UFO has just been discussed.I do not know whether that is dirty,but I made the city where that is everywhere.（注意后半句才含有宾语补足语从句）
If that is nice,I will introduce that to my friend.但只有定语从句中的that才可能既做主语,又是引导词.