单选题 It's been six months. You ______ your research paper by now.
A. have to finish B. must finish
C. can finish D. ought to finish

【正确答案】 B
【答案解析】[解析] 表示“肯定……”意思的助动词must最切合文意。have to和ought to不是表示推测的，而是表示义务的。