You are answering a USMLE-style medical question. Question: A 15-year-old girl comes to the physician because she has not had menstrual bleeding for the past 3 months. Menses had previously occurred at irregular 15–45 day intervals with moderate to heavy flow. Menarche was at the age of 14 years. She started having sexual intercourse with her boyfriend about 3 months ago. Six months ago she had a manic episode, which was treated with risperidone. Her mother has PCOS and her father has diabetes mellitus. She is very conscious of her weight and appearance. She is 171 cm (5 ft 6 in) tall and weighs 79 kg (174 lb); BMI is 27.02 kg/m2. Her temperature is 37°C (98.6°F), pulse is 60/min, and blood pressure is 116/70 mm Hg. The abdomen is soft and nontender. Pelvic examination shows a normal vagina and cervix. Serum hormone studies show: Prolactin 16 ng/mL Thyroid-stimulating hormone 3.8 μU/mL Follicle-stimulating hormone 6 mIU/mL Luteinizing hormone 5.1 mIU/mL Progesterone 0.8 ng/mL (follicular N <3; luteal N >3–5) Testosterone 2.2 nmol/L (N <3.5) A urine pregnancy test is negative. Which of the following is the most likely cause of her symptoms?" Options: A) Uterine fibroids B) Congenital defect of the Mullerian ducts C) Purging behavior D) Anovulation Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.