Question

I am interested in ( )you have said .A.all that B.all what C.thatD.which 为什么不选D

Answer 1

A
all that=what=the thing (that....)
what 引导名词性从句，what既作in的宾语，又作从句的引导词。
没有 all what
C/D成分不全。

Answer 2

which在这里是特指，但是题目没有说明任何交谈的内容