2、先行词有the only, the same, the very修饰时。
例如 The articles are the very ones that should be read.
3、先行词有形容词最高级和序数词修饰时。
例如 This is the best film that I have ever seen.
4、先行词既指人又指物。
例如 We talked about the person and things that we remembered.
5、句中已经有who或which时，避免重复。
例如 Who is the man that is making a speech?
只能用which，不能用that
1、在非限定性定语从句中，无论如何也不能用that
This brunch of carnation, which is wound by silk ribbon ,is the first gift to my mom.
这束康乃馨是送给妈妈的第一份礼物，它被丝带所缠绕。
2、关系代词前面出现介词时
Those days in which you could travel without a passport has gone.
那些你不用带护照可以旅行的'日子一去不复返了。
3、当先行词本身为that（指代）时
what about that which had appeared in recent activities.
那个怎么样，在最近的活动中出现过. (结合具体语境看that所指代的是什么)
4、当先行词是baby, child等词时
Have you notice that child which has lost his way to home in the supermarket ?
在超市，你注意到那个找不到回家路的孩子了吗？
