This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral cavity & Oesophagus, Subject name: ENT
Regurgitation of food back from stomach into oesophagus is prevented by 
Select and explain. 
A. Pinch cock effect of diaphragm, B. Negative intrathoracic pressure, C. Oesophagogastric angle, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Regurgitation of food back from stomach into oesophagus is prevented by: (i) tone of gastro-oesophageal sphincter, (ii) negative intrathoracic pressure, (iii) pinch-cock effect of diaphragm, (iv) mucosal folds, (v) oesophagogastric angle and (vi) slightly positive intra-abdominal pressure. Ref:- Dhingra; pg num:-341