Question

I _________ get on the bus when I heard someone calling me from behind．

A. was to
B. was going to
C. would
D. was about to

Answer 1

答案D
be about to意为“正要”。全句的含义为“我刚要上车，这时我听到有人在背后叫我”。该句特点为：主句是背景，而when从句却是要表达的主要内容，这样主句时态往往是进行时，可用be about to来表示。而其他三项只有表示将来时。
参考：http://www.zuoyebao.com/q/20754