This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'What is the main constituent of the plasma membrane? \nSelect and explain. \nA. Carbohydrate, B. Lipid, C. Phospholipid, D. Protein', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The approximate composition is proteins: 55 percent; phospholipids: 25 percent; cholesterol: 13 percent; other lipids: 4 percent; and carbohydrates: 3 percent. .', 'role': 'assistant'}]