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: Surgery
The principal action of ammonia in syncope is as a: 
Select and explain. 
A. Vasomotor stimulant, B. Respiratory stimulant, C. Vagal stimulant, D. Inhibitor of vasomotor tone
B: Respiratory stimulant
Answer: B: Respiratory stimulant 
Explanation: None