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': 'Entracellular binding site on Na+ - K+ pump is \nSelect and explain. \nA. Na+, B. ATP, C. PO4, D. Ouabain', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Ouabain', 'role': 'assistant'}]