The supervisor could have prevented the accident,( )it beforehand.
A、
has he known
B、
had he known
C、
if he knows
D、
if he knew
【正确答案】:B
【题目解析】:
本题考查的是虚拟语气,不选AC,要判断是对现在还是对过去的虚拟,根据句意,“他之前知道的话,就可以防止事故发生”,整个事件发生在过去,用had done,所以是对过去的虚拟,选B。句意:如果事先知道,监督员本可以防止事故的发生。