This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head & Neck, Subject name: Anatomy
The cricopharyngeal sphincter is how far from the central incisor? 
Select and explain. 
A. 15cm, B. 25cm, C. 40cm, D. 50cm
A: 15cm
Answer: A: 15cm 
Explanation: Ans. is 'a' i.e., 15 cm * Oesophagus shows four contrictions -i) At the beginning at C6 vertebra, the first constriction of the cricopharyngeal sphinctor- 15 cm (6 inches) from incisorii) At the level of T4 vertebra where it is crossed by the aortic arch :-22.5 cm (9inches) from the incisor.iii) At the level of T6 vertebra where it is crossed by left principal bronchus 27.5 cm (11 inches) from incisoriv) At the level of T10 vertebra, its passage through esophageal hiatus of diaphram (lower esophageal sphincter:- 37.5-40 cm (15-16 inches) from incisor