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
[{'content': 'Which of the following retinoids has major role to play in epithelial differenciation? \nSelect and explain. \nA. Retinal, B. Retinol, C. Retinoic acid, D. None of the above', 'role': 'user'}, {'content': "Answer: C \nExplanation: 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", 'role': 'assistant'}]