You are answering a USMLE-style medical question. Question: A 15-year-old girl is brought to the physician because she has not had a menstrual period. There is no personal or family history of serious illness. She is 165 cm (5 ft 5 in) tall and weighs 57 kg (125 lb); BMI is 21 kg/m2. Vital signs are within normal limits. Examination of the breasts shows a secondary mound formed by the nipple and areola. Pubic hair is sparse and lightly pigmented. Abdominal examination shows bilateral firm, nontender inguinal masses. Pelvic examination shows a blind-ended vaginal pouch. Ultrasonography does not show a uterus or ovaries. Which of the following is the most appropriate treatment for this patient's condition? Options: A) Gonadectomy B) Testosterone therapy C) Vaginal dilatory therapy D) Prednisolone therapy Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.