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
[{'content': 'Thickest layer of tear film is: \nSelect and explain. \nA. Mucus layer, B. Aqueous layer, C. Oily layer, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Aqueous layer', 'role': 'assistant'}]