How___that he looked so angry?

题目

How___that he looked so angry?
A.it came about B.did he came about C.was it come about D.did it come about

答案

D.did it come about 是对的
how do it come about that 是 固定用法,相当于why,意思是“为什么.”.其中it是形式主语,真正的主语是后面的that从句
come about 发生的意思