You are answering a USMLE-style medical question. Question: A 55-year-old nulligravid woman comes to the physician because of a 3-day history of heavy vaginal bleeding, requiring more than 5 pads per day. Menopause occurred 1 year ago. She attained menarche at 10 years of age. She has a history of hypothyroidism and type 2 diabetes mellitus. She has smoked 1 pack of cigarettes daily for 20 years but quit 5 years ago. Current medications include levothyroxine and metformin. She is 165 cm (5 ft 5 in) tall and weighs 86 kg (190 lb); BMI is 32 kg/m2. Physical examination shows mild vaginal atrophy and a normal cervix. The uterus and adnexa are nontender to palpation. Transvaginal ultrasonography shows an endometrial thickness of 6 mm. Endometrial biopsy shows non-invasive proliferation of endometrial glands with no nuclear or cytological atypia. Which of the following is the most appropriate next step in management? Options: A) Total hysterectomy B) Estrogen vaginal cream C) Reassurance and follow-up D) Progestin therapy Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.