Have you asked her for the reason____may explain her absence?横线上的答案为什么是that而不是what呀?

题目

Have you asked her for the reason____may explain her absence?横线上的答案为什么是that而不是what呀?

答案

先把这个句子换成陈述句来讲,你就好理解了：
You have asked her for the reason____may explain her absence
主语You 谓语have asked 间接宾语her 直接宾语 reason
简单来说,reason是名词,____may explain her absence做reason的定语从句,翻译过来就是：可以解释他缺席的那个（that）原因
如果填what,就翻译成 可以解释他缺席的什么(what）原因,说不通
词性上来说,reason是名词,what也是名词,两个非组合名词不能连在一起,而that 可以做代词,取代reason在定语从句中做主语,that may explain her absence