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: Pharmacology
[{'content': 'Michaelis Menton constant is: \nSelect and explain. \nA. Concentration of drug at which the reaction velocity is half of maximum, B. Concentration of drug at which the reaction velocity is maximum, C. Both, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]