This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
Meibomian glands secrete which component of sweat- 
Select and explain. 
A. Water {aqueous}, B. Mucin, C. Protein, D. Lipid
D: Lipid
Answer: D: Lipid 
Explanation: Oily layer of tear film. Ref khurana 6th edition REF IMG