—How did your mathematics exam go？
—I thought I ，but in fact I fell behind in the class.
A. should have been the top 10
B. could have been the top 10
C. may have been the top 10
D. need have been the top 10
网友回答
A. should have been the top 10
(答案→)B. could have been the top 10
C. may have been the top 10
D. need have been the top 10
解析：考查虚拟语气。句意：你的数学考试怎么样？——我认为我能进前十名，但是实际上我在班里名落孙山。表示对过去事情的假设，意思是本来能够做某事而没有做，用“could+have+done”，故选B。