None of us was good at swimming so the crossing of this dangerous river was really a.A. m

问题补充：

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

答案：

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。