【开放英语4(英语II(2))-1162网上形考机考题库】 Since this road is wet and slippery this morning, it _____ last night.

【开放英语4(英语II(2))-1162网上形考机考题库】 Since this road is wet and slippery this morning, it _____ last night.
A. must rain
B. was raining
C. may rain
D. must have rained