You are answering a USMLE-style medical question. Question: A 10-year-old boy is brought to his pediatrician after discovering a painless mass in the left testicle. Results from tumor markers and a biopsy are as follows: AFP 350 ng/mL (normal value < 10 ng/mL) hCG 0.4 IU/L (normal value < 0.5 IU/L) Biopsy: Presence of glomeruli-like structures with a central capillary within a mesodermal core, lined by flattened layers of germ cells. What is the most likely diagnosis in this patient? Options: A) Classic seminoma B) Choriocarcinoma C) Teratoma D) Yolk sac tumor Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.