None of us was good at swimming, so the crossing of this dangerous river was really a .
A. motivation
B. symptom
C. conflict
D. challenge
网友回答
A. motivation
B. symptom
C. conflict
(答案→)D. challenge
解析：考查名词辨析：A．motivation动机B．symptom症状C．conflict 冲突D．challenge挑战，句意：我们没有人擅长游泳，所以过这条危险的河真是挑战。选D。