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': 'Intravenous administration of norepinephrine in a patient already taking an effective dose of atropine will often: \nSelect and explain. \nA. Increase heart rate, B. Decrease total peripheral resistance, C. Decrease pupil size, D. Has no effect on cardiovascular system', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]