引导定语从句的关系代词who,which有时可与such that互换使用。但在下面情况，一般只用 such that。下面是总结几种情况：
一、当先行词为不定代词anything, everything, nothing, any, little, one, few, much, all, none等时。如：
e isn't much that I can do.
is one of the few that can work it out in five minutes.
二、当先行词是形容词最高级或被形容词最高级修饰时。如：
book is the best that I have read.
is the biggest laboratory that we have ever built in our university.
三、当先行词是序数词或其被序数词修饰时。如：
is the third one that I've bought.
is the first place that I've ever visited.
四、当先行词被the very, the only等词修饰时。如：
this the very museum that you visited the other day?
is the only book that I need at present.
五、当先行词包含了人和事物两方面的含义时。如：
They talked of things and persons that they remembered in the school.
六、当先行词被same修饰，且指“同一物品”时。如：
She is wearing the same dress that she wore yesterday.
七、关系代词在定语从句中作表语时。如：
is no longer the place that it used to be.
is not the man that he was.
八、当主句是以who,which开头的特殊疑问句或先行词是who时。如：
h is the book that he bought yesterday?
that you have ever seen can beat him in the game?
