At last hefinish the work ahead of time.A. couldB. was able toC. could have doneD. would h

问题补充：

At last hefinish the work ahead of time.

A. could

B. was able to

C. could have done

D. would have been able to

答案：

A. could

(答案→)B. was able to

C. could have done

D. would have been able to

解析：此句检测对can和be able to辨析使用的能力。从时态上讲，can只有过去，而be able to可用于各种时态；从语意上讲，be able to的过去可表示“设法完成某事”，相当于managed to do sth.而could则无此用法。