题目内容：

the suspect couldn't answer the question_____he had been doing when the criminal case took place
A,that B,whether C,what D,where

优质解答

选C,同位语从句中有个doing,它是及物动词,必须得接个事物性质的词,只有what了,同位语从句中that可以省略,what sb.do就是某人所做的事