You are answering a USMLE-style medical question. Question: A 14-year-old girl comes to the physician with her father for evaluation of her short stature. She feels well overall, but is concerned because all of her friends are taller than her. Her birth weight was normal. Her father reports he had a short stature during his teenage years; he is currently 177 cm (5 ft 10 in) tall. She is at the 2ndpercentile for height and 35th percentile for weight. Breast development is Tanner stage 2. Pubic and axillary hair is absent. An x-ray of the left hand and wrist shows a bone age of 11 years. Which of the following is the most appropriate next best step in management? Options: A) Pelvic ultrasound B) Measure serum dehydroepiandrosterone levels C) Reassurance and follow-up D) MRI of the brain Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.