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: Biochemistry
Retinol is a primary alcohol containing:- 
Select and explain. 
A. Alpha-ionone ring, B. Beta-ionone ring, C. One isoprenoid unit, D. Two double bonds
B: Beta-ionone ring
Answer: B: Beta-ionone ring 
Explanation: Retinol (vitamin A alcohol): 

lt is a primary alcohol containing beta-ionone ring. 
The side chain has two isoprenoid units, four double bonds and one hydroxyl group. 
Retinol is present in animal tissues as retinyl ester with long chain fatty acids

Key Concept:
Retinol is a vitamin A (alcohol containing beta-ionone ring)