This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'When the sympathetic nervous system is activated \nSelect and explain. \nA. Norepinephrine is released by the vascular smooth muscle cells, B. Acetylcholine is released onto vascular smooth muscle cells, C. Norepinephrine is released from axons onto the aeriolar wall, D. The aerioles constrict because nitric oxide production is suppressed', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Nerve fibers, not vascular smooth muscle, release norepinephrine. The norepinephrine from the sympathetic nerves simply diffuses from the axons and binds to specific receptors on smooth muscle cells.', 'role': 'assistant'}]