This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
As deglutition involved voluntary and involuntary stages, so among the following, which structure limits the size of bolus swallowed: 
Select and explain. 
A. Soft palate, B. Posterior pharyngeal pillars, C. Upper esophageal sphincter, D. Larynx
B: Posterior pharyngeal pillars
Answer: B: Posterior pharyngeal pillars 
Explanation: None