This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which of the following combinations of biologically active molecules does vitamin A consist of? 
Select and explain. 
A. Retinol, retinal and retinoic acid, B. Retinol, retinal and tetrahydrofolate, C. Retinol, Iconjugase and retinoic acid, D. PABA, retinal and retinaldehyde
A: Retinol, retinal and retinoic acid
Answer: A: Retinol, retinal and retinoic acid 
Explanation: The term retinoids is often used to include the natural and synthetic forms of vitamin A Retinol, retinal and retinoic acid are regarded as vitamers of vitamin A. beta-Carotene (provitamin A): This is found in plant foods ref Satyanarayana 4th ed page 119