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：情景对话句意为：如果他们不走一整天，他们就不会感到累
If引导的虚拟语气，从此题可判断为对过去事件的虚拟，故从句的时态应用过去完成进行时，主句用would+动词原形
