when do you think----leave for shanghai?

问题描述:

when do you think----leave for shanghai?
A.should I B.that I should
C.I should D.which I should
这题为什么选C,不选其他的了,
怎么分析题目的结构.

正确答案:A
do you think 是插入语,可以省略.就成了:When should I leave for Shanghai?