问题
选择题
Even the top students in our class can't work out this problem. So it _____ be very difficult. [ ]
A. need
B. may
C. can
D. must
答案
答案：D
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Even the top students in our class can't work out this problem. So it _____ be very difficult. [ ]
A. need
B. may
C. can
D. must
答案：D