<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 16-year-old girl is brought to the physician by her mother because she has not attained menarche. She has no history of serious illness. She is at 50th percentile for height and weight. Examination shows no breast glandular tissue and no pubic hair development. The remainder of the examination shows no abnormalities. A urine pregnancy test is negative. An ultrasound of the pelvis shows no abnormalities. Which of the following is the most appropriate next step in management?? A: GnRH stimulation test, B: Reassurance, C: Progesterone challenge test, D: Serum FSH level, E: Serum testosterone level,  <response>: This is a question about primary amenorrhea in a 16-year-old girl. Based on the information provided, she has no signs of pubertal development and her height and weight are normal. The workup so far including pelvic ultrasound and pregnancy test has been unrevealing. The next step would be to check hormones to evaluate for delayed puberty vs primary ovarian insufficiency. FSH levels will help distinguish between these two causes - elevated FSH would indicate ovarian insufficiency while normallow FSH would point towards constitutional delay of puberty. The other answer choices are less useful at this stage.D: Serum FSH level 