I couldn't help____ when hearing the funny story为什么选laughing

I couldn't help____ when hearing the funny story
为什么选laughing

can't help doing sth.(忍不住/情不自禁去做某事）
1.can’t help doing sth．和can’t help but do sth 表示“不得不、禁不住做某事”,
We couldn't help laughing when we heard the funny story.
2.can’t help to do sth．表示“不能帮助做某事”,
I can't help (to) wash the dishes because I am busy preparing for the entrance exams.