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 retinoids has major role to play in epithelial differenciation? 
Select and explain. 
A. Retinal, B. Retinol, C. Retinoic acid, D. None of the above
C: Retinoic acid
Answer: C: Retinoic acid 
Explanation: Active Forms of Vitamin A Function Retinol Reproduction Retinal Vision Retinoic acid Epithelial differentiation, gene expression, growth and development Reference: Harper's Illustrated Biochemistry 31st edition