You are answering a USMLE-style medical question. Question: A 29-year-old man comes in for evaluation of infertility. He has been trying to conceive for over 2 years with his wife and previous evaluation of his wife's fertility revealed no abnormalities. Physical exam reveals a tall man with long extremities, sparse body hair, gynecomastia, and small testes. Laboratory studies reveal increased serum follicle-stimulating hormone concentration and an increased estradiol:testosterone ratio. Genetic studies reveal a cytogenetic abnormality. If this abnormality was inherited from the patient's father, at which stage of spermatogenesis did this error most likely occur? Options: A) Primary spermatocyte B) Secondary spermatocyte C) Spermatid D) Spermatozoon Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.