You are answering a USMLE-style medical question. Question: A 33-year-old woman at 17-weeks gestation comes to the physician for evaluation of a painless mass in the right breast for the last 3 weeks that has not increased in size. Physical examination shows dense breasts and a 2.5-cm rubbery, mobile mass that is nontender in the upper outer quadrant of the right breast. A biopsy of the mass shows rounded contour with overgrowth of fibrous and glandular tissue. Which of the following is the most likely diagnosis? Options: A) Fibroadenoma B) Normal pregnancy-related changes C) Fat necrosis D) Phyllodes tumor Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.