An unidentified wit once said, "laugh, and the world laughs with you. Snore, and you sleep

alone. " Yet snoring is far from a laughing matter, as those unfortunates with good hearing, who are rightly subjected to the sounds of the snoring disorder, will testify. It has been estimated that one of eight Americans snores: this means that there are approximately 21 million people — women as well as men — who render an unpleasant sound when they are asleep. And assuming that each snorer disturbs the sleep of at least one other person, it necessarily follows that there are 21 million unhappy listeners. While a sleeping person breathes, either in or out, several structures in his nose and throat generate the snoring. The sounds, coming from the soft palate and other soft structures of the throat, are caused by vibratory responses to inflowing and outflowing air. When the soft tissues of the mouth and throat come close to the lining of the throat, the vibrations that occur are caused by the position of the tongue. In short, the noise made by snoring can be compared to the noise when breezes flutter a flag on a pole. The frequency of the vibrations depends on the size, density, and elasticity of the affected tissues and on the force of the air flow. Although it is usually the process of in haling or exhaling through the mouth that cause snoring, short snores come from the nose of an open-mouthed sleeper. In all fairness to snorers, however, it should be emphasized that snoring is an involuntary out which stops as the offender is awakened.

The snoring is caused by______.

A．the soft palate and other structures of the throat

B．the inflowing and outflowing air through the nose

C．the inflowing and outflowing air through mouth

D．the vibrations as a result of the inflowing and outflowing air