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: Physiology
Rafts in cell membrane are rich in which of the following? 
Select and explain. 
A. Cholesterol, B. Linoleic acid, C. Protein, D. None of the above
A: Cholesterol
Answer: A: Cholesterol 
Explanation: Some areas of the cell membrane are especially rich in cholesterol and sphingolipids and have been called rafts. These rafts are probably the precursors of flask-shaped membrane depressions called caveolae (little caves) when their walls become infiltrated with a protein called caveolin that resembles clathrin. There is considerable debate about the functions of rafts and caveolae, with evidence that they are involved in cholesterol regulation and transcytosis. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 2.