he is good at _______ 中的横线填swim还是swimming?

问题描述:

he is good at _______ 中的横线填swim还是swimming?

当然是 swimming
因为be good at doing sth 固定用法‘ 擅长于……’ AT是介词,介词后的动词要用ING形式.
加油!不明白再问!