This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Biconcave shape of RBC helps by \nSelect and explain. \nA. Increasing flexibility, B. Increasing surface area, C. Carrying more Haemoglobin, D. Passing easily through smaller capillaries', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The shapes of RBCs can change remarkably as the cells squeeze through capillaries. Actually, the RBC is a "bag" that can be deformed into almostany shape.', 'role': 'assistant'}]