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
Thinnest layer of tear film 
Select and explain. 
A. Mucus layer, B. Aqueous layer, C. Lipid layer, D. Oily layer
A: Mucus layer
Answer: A: Mucus layer 
Explanation: Thickest - Aqueous layer.
Thinnest - Mucus layer.