参考答案：C

解析：[听力原文]Laughter can even provide a kind of pain relief. Scientists had proved that laughter produces endorphins -- chemicals in the body that relieve pain. They divided 40 university students into four groups. The first group listened to a funny cassette for 20 minutes. The other three groups listened to either an informative tape, or a cassette intended to relax them, or no tape at all. Scientists found that if they produce pain in the students, those who had listened to the humorous tape could tolerate the discomfort for much longer.

[分析]： 主旨题。 本段开宗明义说Laughter can even provide a kind of pain relief 即开怀大笑可以缓解疼痛，然后以科学实验作为支持性细节，最后以实验结果强调了本段结论Scientists found that if they produce pain in the students，those who had listened to the humorous tape could tolerate the discomfort for much longer 即科学家发现如果他们对学生们施以疼痛，那些听过幽默故事磁带的学生忍受疼痛的时间更长些。由此可见，选项C的内容与原文意思相符，因此是正确答案。[解题关键] 着重掌握对段落首尾句的理解。段落首句往往点明本段主题，而尾句往往是结论句，概括全段主要内容。