——why were you late for the ceremony of the 2010 shanghai world expo?

问题描述:

——why were you late for the ceremony of the 2010 shanghai world expo?
——a visitor arrived just as we ____for the airport
A start out
B had started out
C were starting out
D would start out
为什么用过去进行时?

动作发生的时间和arrived同时进行,所以用过去式.意思就是我们刚想走的时候有人来了,就是这样.