A likely reason why a to and fro motion, such as that encountered during airplane flights or in an automobile ride over a bumpy road, tends to cause nausea and vomiting, is because during such motions:

• A. Much air is swallowed and the stomach becomes distended
• B. The stomach is more likely to develop reverse peristalsis
• C. The cerebral cortex can no longer inhibit an intrinsic tendency of the brainstem to cause vomiting
• D. Vestibular reflex eventually excite a chemoreceptor trigger zone in the medulla