A prosperity which / that had never been seen bef

Question

A prosperity which / that had never been seen before appears in the countryside.
为什么不能用what

Answer 1

which / that 指代先行词 prosperity，在定语从句中做主语，且指物所以要用which或that。

引导定语从句的关联词包括关系代词和关系副词。关系代词有that, which, whose, who, whom, as；关系副词有when, where, why。
而你所问的what，是不能用在定语从句中的，要用在名词性从句中，例如宾语从句中，I don't know what you said.

Answer 2

which that引导定语从句修饰主语 a prosperitywhich是先行词,在从句中做主语。
what是不能引导定语从句的。

Answer 3

What 在定语从句中相当于the thing(先行词) that, 此句中只需要which/that 就可以了 例what (the thing that) you told me before is wrong.

Answer 4

你是猪吗？本回答被提问者采纳

Answer 5

主语的意思是：繁荣，不是物，所以不能用what