So uncertain （）about the background of his audience that he didn’t know how to start his lecture.
A、
he would become
B、
would he become
C、
he had become
D、
did he become
【正确答案】：D
【题目解析】：
他不熟悉观众的背景，以致于他不知道如何开始他的演讲。So ...that...是倒装句，排除A,C。因为that从句中用的过去时，所以选D。