When we watched the clown performing, we could not ( ) laughing

When we watched the clown performing, we could not ( ) laughing.
A、break out
B、repress
C、help
D、burst into
【正确答案】：C
【题目解析】：couldn't help doing sth. 禁不住做某事，句子含义时当我们看小丑表演时，我们忍不住笑个不停。