This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Biochemistry
What serves as a precursor of testosterone? 
Select and explain. 
A. Aldosterone, B. Estrone, C. Methyltestosterone, D. Pregnenolone
D: Pregnenolone
Answer: D: Pregnenolone 
Explanation: Cholestrol is first acted upon by desmolase and 6 carbon unit cleaved off,forming the 21 carbon steriod, pregnenolone It is common precursor for all steriod hormonesRef: DM Vasudevan, 7th edition, page no: 664, 665, 666