1. that用作先行词时定语从句用什么引导
that后接定语从句时，通常用关系代词which来引导。如：
I have that which you gave me. 我有你给我的那个。
That which many people say is not always true. 很多人说的并不表示一定是真的。
注：that which是一个比较正式的用法，在通常情况下会用what代替。如：
What many people say is not always true. 很多人说的并不表示一定是真的。
另外注意，that后可接定语从句，但this后习惯上不接定语从句。
2. those用作先行词时定语从句用什么引导
those后接定语从句时，通常用关系代词who来引导。如：
Those who do not wish to go need not go. 不愿去的人不需要去。
It is said that those who eat the most are the least healthy. 据说吃得最多的人身体最差。
另外注意，those后可接定语从句，但these后习惯上不接定语从句。