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': 'After adding Drug A to an enzyme - substate reaction, Km remains same and Vmax decreases.\n Drug A is a \nSelect and explain. \nA. Competitive antagonist, B. Non competitive antagonist, C. Agonist, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In Non competitive Antagonism: Km remains same, Vmax decreases.\nIn Competitive Antagonism: Km increases, Vmax remains same.', 'role': 'assistant'}]