This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Testosterone production is mainly contributed by: 
Select and explain. 
A. Leydig cells, B. Seolie cells, C. Seminiferous tubules, D. Epididymis
A: Leydig cells
Answer: A: Leydig cells 
Explanation: Testosterone is a Cl 9 steroid that is synthesized from cholesterol within the interstitial Leydig cells. Ref: Ganong's Review of Medical Physiology, 22nd Edition, Pages 424-25; Good Clinical Practice in Assisted Reproduction By Paul Serhal, Caroline Oveon, 2004, Page 25.