问题补充:
The tourists didn’t stop to rest at each station because it them down.
A. had slowed
B. would slow
C. should have slowed
D. would have slowed
答案:
A. had slowed
B. would slow
C. should have slowed
(答案→)D. would have slowed
解析:would have slowed 是虚拟语气,其后省略if they had stopped at each station