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
β2 selective agonists are often effective in: 
Select and explain. 
A. Angina due to coronary insufficiency, B. Asthma, C. Delayed labour, D. All the above
B: Asthma
Answer: B: Asthma 
Explanation: None