His father often tells him in that river because it’s dangerous.A. not to swimB. not swim

问题补充：

His father often tells him in that river because it’s dangerous.

A. not to swim

B. not swim

C. swim

D. to swim

答案：

(答案→)A. not to swim

B. not swim

C. swim

D. to swim

解析：不定式的否定式通常是在不定式符号to前面加not，tell后接带to的不定式。根据下文因为太危险了。前文意思为：他的父亲告诉他不要去在那条河里面游泳。故选A。