A 56-year-old man with a 60 pack-year cigarette smoking history, recent 5-lb unintended weight loss, and a 3-month history of new-onset symptoms of peptic disease presents for care. He is taking no medications on a regular basis and reports drinking approximately six 12-oz beers per week with no more than 3 beers per day. Physical examination is unremarkable except for mild pharyngeal erythema and moderate epigastric tenderness without rebound. The most helpful diagnostic test at this point in his evaluation is a:_________.

A. upper endoscopy.

B. barium swallow.

C. evaluation of H. pylori status.

D. esophageal pH monitoring.