This is all ( )I know about the accident.填that或what请说明为什么
问题描述：
This is all ( )I know about the accident.
填that或what请说明为什么
答
what
答
that
all that=what
答
all that
that是关系代词,引导定语从句,它在定语从句中作know的宾语,因而可以把它省略.what引导从句时它的意思是‘所……的……’,它的意义中也包含‘所有’的意思,what = all that,因此what的前面不能有all,换句话说,all后面不能用what