I was on the highway when this car went past followed by a police car.They at least 150 k

I was on the highway when this car went past followed by a police car.They at least 150 kilometers an hour.
A. should have been doing
B. must have been doing
C. could have done
D. would have done

A. should have been doing(答案→)B. must have been doingC. could have doneD. would have done解析：此题考查虚拟语气。根据句意，我对这辆车和紧随其后的警车的速度不能确定，只能推测。“must have been doing” 表肯定，推测车速至少在每小时150千米。易错点:C项意为“本来能……(暗示实际上没能或没做)”。

这下我知道了