You are answering a USMLE-style medical question. Question: A 35-year-old woman presents to the office because she has felt a small painless mass in her neck which has been slowly growing. She has no relevant past medical history. Her vital signs are within normal limits. On physical exam of the thyroid gland, a solitary nodule is palpated. It is fixed to the surrounding tissues and nontender. TSH is normal, and antithyroid antibodies are negative. Which of the following is the most likely cause of this patient’s symptoms? Options: A) Endemic goiter B) Follicular carcinoma C) Hashimoto thyroiditis D) Papillary carcinoma Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.