单选题 The conference ______ a full week by the time it ends.
A. must have lasted B. will have lasted
C. would last D. has lasted

【正确答案】 A
【答案解析】[解析] 句意是：到它结束时，大会一定是已经开了整整一周的时间。by加时间的句子用现在完成时。这句话用情态动词must表示推测。根据句意推出正确答案是A选项。