问题补充：
They so tired if they for a whole day.
A. wouldn’t feel, didn’t walk
B. wouldn’t feel, weren’t walking
C. wouldn’t be feeling, weren’t walking
D. wouldn’t be feeling, hadn’t been walking
答案：
A. wouldn’t feel, didn’t walk
B. wouldn’t feel, weren’t walking
C. wouldn’t be feeling, weren’t walking
(答案→)D. wouldn’t be feeling, hadn’t been walking
解析：考查虚拟，由后面的时间状语，可以知道动作发生在过去，由后面的if，对过去的一种虚拟，所以后面用过去完成进行时，所以选D
