The experts present at the conference all insisted that greenhouse gas emission be reduced from now on．
A. must
B. will
C. /
D. can
网友回答
A. must
B. will
(答案→)C. /
D. can
解析：句意：出席会议的专家都坚持温室气体排放从现在起要减少。动词insist做为“坚持要求”的时候，后面的宾语从句，用虚拟语气，谓语是should do，should可以省略，所以选C。