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': 'β2 selective agonists are often effective in: \nSelect and explain. \nA. Angina due to coronary insufficiency, B. Asthma, C. Delayed labour, D. All the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]