“Show me your permit, please.” “Oh, it’s not in my pocket. It .”
A. might fall out
B. could fall out
C. should have fallen out
D. must have fallen out
网友回答
A. might fall out
B. could fall out
C. should have fallen out
(答案→)D. must have fallen out
解析：既然“通行证现在不在口袋里”，那么它“掉出去”应发生在过去，故排除A和B。比较选项C和D所表示的意思，选D更恰当。