WHY DO PEOPLE YAWN?

作     者：Randy Smith 杨一铮 

出 版 物：《大学英语》 (College English)

年 卷 期：1989年第2期

页      面：25-26页

主　　题：WHY DO PEOPLE YAWN 

摘      要：(1) Why do people yawn? No one really knows for sure. Most people believe they yawn because they are tired. During yawning, air is breathed in, the throat cavity enlarges, and muscles in the neck and jaws contract. The pressure of these contractions can often be felt in the middle ear where a popping sound can be heard. A11 these things