The problems at the meeting tomorrow are really hard to solve．
A. discussed
B. to discuss
C. to be discussed
D. discussing
网友回答
A. discussed
B. to discuss
(答案→)C. to be discussed
D. discussing
解析：The problems 与discuss之间是被动的关系，应用被动语态；tomorrow这个时间状语决定应该是将来的事情，不定式可以表示将来，因此选C。