You are answering a USMLE-style medical question. Question: An investigator is studying the cell morphologies of the respiratory tract. He obtains a biopsy from the mainstem bronchus of a patient. On microscopic examination, the biopsy sample shows uniform squamous cells in layers. Which of the following best describes the histologic finding seen in this patient? Options: A) Metaplasia B) Normal epithelium C) Dysplasia D) Anaplasia " Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.