【题目】— Why was Tom so happy yesterday?
— Lacking work experience ________ him his job, but luck smiled on him.
A. could have cost B. should have cost C. must have cost D. may have cost
在线课程【答案】A
【解析】考查情态动词加动词不定式的完成式。上句：昨天汤姆为什么如此高兴？下句：缺乏工作经验本来可能使他失去了工作，但是幸运向他微笑。could have done可能已经做了某事，故选A。