The two presidents agree with each other on the whole but much remains at the following

问题补充：

The two presidents agree with each other on the whole, but much remains at the following meeting.

A. to discuss

B. discussing

C. to be discussed

D. discussed

答案：

A. to discuss

B. discussing

(答案→)C. to be discussed

D. discussed

解析：句意：两个总统基本上都同意了，但是很多仍然将在下次会议上被讨论。agree with 同意；on the whole基本上，大体上；remain to be done有待于被做，这里much与discuss是被动关系，并且用动词不定式表示将来，故选C。