His car hit against one on the left on the expressway in the fog and __off the elevated road to the ground.

His car hit against one on the left on the expressway in the fog and __off the elevated road to the ground.
A.down did it roll. B.down it rolled C.down rolled it D.it down rolled
为什么要倒装选B不选D
and后面是倒桩怎么看出来的。。。