Evening was____as I took the roa

Evening was____as I took the road over Mountain Top.
A、setting out
B、setting in
C、setting down
D、setting off
【正确答案】：B
【题目解析】：B当我行于山顶公路时夜幕降临。词组辨析题，要求考生能分辨几个词组的意义差别。set in指开始发生或出现; set off指导致发生, 开始旅程; set down指记录写下; set out指着手, 开始旅程。