As与which的区别
在限制性定语从句中，名词前有such和the same修饰时，关系代词用as,不能用which。如：
He is not such a fool as he looks.他不像看上去那么傻。
Don’t read such books as you can’t understand.不要读这样的书，你无法理解。
在非限制性定语从句中，as和which都可以指代前面整个主句。如果有“正如，象”的含义，并可以放在主句前，也可以放在后面，那么用as；而which引导的从句只能放主句后，并无“正如”的意思。
They won the game, as we had expected. 他们如我们所料赢得了比赛
They won the game, which we hadn’t expected.他们赢了这场比赛，这是我们未预料到的。
As is well known, he is a famous film star in the 1980s. 众所周知，他是20世纪80年代的著名电影明星。
What 与that的区别
What 有“所……的”含义，而that 则没有
The thing (that) he did is obvoiusly right .他做的事显然是对的。
What he did is obvoiusly right .他所做的显然是对的。
That he did it is not strange at all.他这么做一点也不奇怪。
Some of whom (which );与some of them 的区别
Some of whom (which)中的whom \which 是关系代词，能用于定语从句；而some of them 中的them是普通代词，只能用于并列句
I have many friends,some of whom are businessmen.我有许多朋友，其中一些是商人
I have many friends,and some of them are businessmen.我有很多朋友，其中有些是商人。
She has many books, only one of which is interesting. 她有许多书,只有一本是有趣的。
She has many books, and only one of them is interesting.她有许多书，其中只有一本有趣。
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