You are answering a USMLE-style medical question. Question: A 72-year-old Caucasian male presents to your office with dysphagia and halitosis. If this patient is also found to have cricopharyngeal muscle dysfunction, which of the following is the most likely cause of his presenting symptoms? Options: A) Gastroesophageal reflux disease B) Esophageal candidiasis C) Meckel's diverticulum D) Zenker's diverticulum Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.