You are answering a USMLE-style medical question. Question: A 14-year-old boy is brought to the physician for evaluation of his sense of smell. Two days ago, his mother found that he had left the gas on in the kitchen, and he was unable to smell the odor of the gas. As a child, he was consistently in the 40th percentile for height; now he is in the 15th percentile. He had bilateral orchidopexy for cryptorchidism as an infant. The patient is unable to identify several common odors when presented with them. Physical examination shows sparse axillary and pubic hair and Tanner stage 1 genitals. Which of the following is the most likely underlying cause of the patient's condition? Options: A) Compression of pituitary stalk B) Hyperprolactinemia C) Impaired migration of GnRH neurons D) Decreased thyroxine production Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.