This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood Physiology, Subject name: Physiology
Which of the following proteins is responsible for flexibility of RBCs? 
Select and explain. 
A. Spectrin, B. Ankyrin, C. Band 3, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: The spherocytosis is caused by mutations in proteins that make up the membrane skeleton of the erythrocyte, which normally maintains the shape and flexibility of the red cell membrane, including spectrin, the transmembrane protein band 3 and the linker protein, ankyrin.