Now that there are still some problems remaining , we have to work extra hours tonight
A. solved
B. solving
C. to be solved
D. to solve
网友回答
A. solved
B. solving
(答案→)C. to be solved
D. to solve
解析：表示将来，故用不定式，且solve与其逻辑主语some problems之间是被动关系，故用不定式的被动式。