定语从句中that这时候能用吗

Question

vitamin D gets produced when animals are exposed to direct sunlight， for which reason ，it is always advisable to give them chances to spend time in the sun.
这句话中 for which reason用for what代替可以吗？为什么不能用for that reason？

Answer 1

不能。
此处为非限制定语从句，先行词是前面句子，作介词for宾语，要用关系代词which，不能用that。what不能用于定语从句。追问

哦哦哦谢谢

如果用for what前面要加一个and对吧

追答

what不能用来引导定语从向

句

Answer 2

此处for which reason不能用for what代替，此句中which引导非限制性定语从句，指代的是前文整个句子，what没有该用法。
同样for which reason也不能用for that reason代替，因为that不能引导非限制性定语从句。

Answer 3

定语从句的引导词里没有what！