Scenario Yawning Is a Reflexive Action That Is Often Associated with with Sleepiness

Scenario
Yawning is a reflexive action that is often associated with sleepiness. When a person yawns, the mouth opens, and a longer than normal breath of air is inhaled, followed by a longer than normal exhalation. Hypothesizing that yawning has a regulatory mechanism similar to breathing, scientists conducted an experiment on college students to test the effect of existing carbon dioxide levels on yawning.
-The structure where the respiratory and digestive systems meet expands during a yawn. What is the name of this structure?

A) bronchus
B) larynx
C) pharynx
D) trachea