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: Ophthalmology
Metabolically active corneal layer is: 
Select and explain. 
A. Epithelium, B. Stroma, C. Descemet's membrane, D. None of the above
A: Epithelium
Answer: A: Epithelium 
Explanation: Ans. Epithelium