后接定语从句时用this还是that？

问题描述

请看下面一题：

They say the only real knowledge is _______ which can be measured.

A. this B. that

答案是A还是B？问题的关键是：后接定语从句时用this还是that？

老师答疑

张老师：

that可以作为先行词被定语从句限制，其后可用which, 但不可用who/that. 没见过this后跟定从的情况。
that which 中的 which 为关系代词，其意为“… 的事或物”，这是一种比较正式的用法，它通常可以用what代之。如：
That which (=What) many people say is notalways true. 很多人说的话并不表示一定是真的。 
That which (=What) I say anddo is my own affair. 我说什么做什么是我自己的事。
They say the only real knowledge is that which can be measured. 据说唯一真实的知识是可以检验的知识。