Those responsible for the accident be punished while those contributing to solving the problems be rewarded, promised the official then and there.
A. need
B. may
C. can
D. shall
网友回答
A. need
B. may
C. can
(答案→)D. shall
解析：句意：这位官员当场允诺：事故的责任人将受到惩罚，而对于解决这个问题做出贡献的人将给予奖励。need需要；may可以；can能够；shall表示命令，威胁等。这里是shall表示命令，故选D。