The parents will use ____they have to send their son to technical school 为什么只能用what ,而不用all
问题描述：
The parents will use ____they have to send their son to technical school
为什么只能用what ,而不用all
答
我觉得可以用all，这两个都可以，表示的都是一个意思。
答
The parents will use ____they have (to send their son to technical school)
what=all that
加all则all为定语从句先行词that不可省略