Sheldon could have defeated Howard in the match, but he too careless at the last minute.
A. is
B. was
C. has been
D. had been
网友回答
A. is
(答案→)B. was
C. has been
D. had been
解析： 句意：Sheldon本可以在比赛中打败 Howard的，但是他最后一分钟太粗心了。前面的could have defeated是对过去情况的虚拟，but后面的内容是过去的事实，用一般过去式，所以选B。