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
Biconcave shape of RBC’s is helpful because: 
Select and explain. 
A. Easily passage through capillaries, B. Roulex formation., C. Increased surface area for a given diameter., D. None.
A: Easily passage through capillaries
Answer: A: Easily passage through capillaries 
Explanation: Guyton-419
Normal 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.