Esophagus is constricted at 4 anatomic locations. Narrowest pa of esophagus lies at which of the following constriction?

Narrowest pa of esophagus is at its commencement at the cricopharyngeal sphincter which is 15cm from the incisor teeth. Other sites of esophagus where it is slightly constricted includes:Crossing by the aoic arch which is 22cm from the teeth.Crossing by the left principal bronchus which is 27cm from the teethAt the opening in the diaphragm which is 38cm from the teeth