You are answering a USMLE-style medical question. Question: A 58-year-old white man with hypertension and type 2 diabetes mellitus comes to the physician because of a 3-month history of a painless lesion on his lower lip. He has smoked one pack of cigarettes daily for 20 years. He has worked as a fruit picker for the past 25 years. His current medications include captopril and metformin. Examination of the oral cavity shows a single ulcer near the vermillion border. Which of the following is the most likely diagnosis? Options: A) Squamous cell carcinoma B) Aphthous stomatitis C) Actinic keratosis D) Traumatic ulcer Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.