Investigation of choice for Zenker's diveiculum is:

Ans is `d' i.e. Barium Swallow "Once suspected, the diagnosis is established by a barium swallow. Endoscopy is usually difficult in the presence of a cricopharyngeal diveiculum, and potentially dangerous, owing to obstruction of the true esophageal lumen by the diveiculum and the attendant risk of \\diveicular peiforation."- Schwaz