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
Entracellular binding site on Na+ - K+ pump is 
Select and explain. 
A. Na+, B. ATP, C. PO4, D. Ouabain
D: Ouabain
Answer: D: Ouabain 
Explanation: D i.e. Ouabain