（） surprised me most was（） they had finished it so

问题补充：

surprised me most was they had finished it so quicklywhat；whatThat；thatWhat；thatThat；what请问选哪个啊?感激 说下原因

答案：

what,that

what引导名词从句,意思是.的本句意思最让我惊讶的...,

that引导名词从句(在这里是表语从句)

======以下答案可供参考======

供参考答案1:

What that