问题补充：
He the best person you had been expecting for the job, but who else ?
A. may not be; could be
B. couldn’t be; might be
C. might not have been; could have been
D. mustn’t be; must have been
答案：
A. may not be; could be
B. couldn’t be; might be
(答案→)C. might not have been; could have been
D. mustn’t be; must have been
解析：句意：他可能不是你过去所期望的胜任这个工作最好的人，但是还有谁可能是呢？might not have been过去可能没有做某事，could have been过去能够做某事，根据句意，故选C.
