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