This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of lipid, Subject name: Biochemistry
The double bond in cholesterol structure is found in 
Select and explain. 
A. Ring D, B. Ring C, C. Ring B, D. Ring A
C: Ring B
Answer: C: Ring B 
Explanation: structure of cholesterol Cholesterol is a 27-carbon compound containing a steroid nucleus, which resembles a phenanthrene ring (rings A, B, C) to which a cyclopentane ring (ring D) is attached Methyl groups are attached at carbons 10 and 13. A side chain is attached at carbon-17. A hydroxyl group is attached at carbon-3. Double bond is present in Ring B. Reference: Harper's Illustrated Biochemistry 30th Edition Pg 219