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
[{'content': 'Biconcave shape of RBC’s is helpful because: \nSelect and explain. \nA. Easily passage through capillaries, B. Roulex formation., C. Increased surface area for a given diameter., D. None.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Guyton-419\nNormal red blood cells, are biconcave discs having a mean diameter of about 7.8 micrometres and a thickness of 2.5 micrometres at the thickest point and 1 micrometre or less in the centre. The shapes of red blood cells can change remarkably as the cells squeeze through capillaries.', 'role': 'assistant'}]