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': 'Which of the following can reverse one or more smooth muscle effects of circulating histamine in humans? \nSelect and explain. \nA. Granisetron, B. Adrenaline, C. Ranitidine, D. Sumatriptan', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Adrenaline is a physiological antagonist of histamine. It reverses bronchoconstriction caused by histamine. Ranitidine is an H2 antagonist that decreases gastric acid secretion but has no effect on smooth muscles.', 'role': 'assistant'}]