问题补充：
-----Did you have a hard time traveling back home?
-----Yes, it for four days when I arrived in Guiyang and all the roads covered with ice.
A. snowed, were
B. was snowing, had been
C. had been snowing, had been
D. had snowed, were
答案：
A. snowed, were
B. was snowing, had been
C. had been snowing, had been
(答案→)D. had snowed, were
解析：考察时态。句意：—在旅游回来的路上，你们过的很艰难是吧？—是的。当我们到达贵阳，因为已经下了四天的雪，所有的路上都是冰。根据句中的arrived说明路上都是冰这是在我们到贵阳的时候的事情，所以使用一般过去时。已经下了四天的雪是在我们到达之前，故使用过去完成时。故D正确。
