问题补充：
He writing the paper now. He hadn’t written a single word when I left him ten minutes ago.
A. shouldn’t be
B. can’t have finished
C. can’t be
D. mustn’t have finished
答案：
A. shouldn’t be
(答案→)B. can’t have finished
C. can’t be
D. mustn’t have finished
解析：查情态动词。“can’t have + 过去分词”表示对过去情况的可能性推测，此处意为“不可能已完成”。
