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
Contraindications of beta blockers are:  a) Asthma b) Heart block  c) Hypertension d) Arrhythmia 
Select and explain. 
A. b, B. ab, C. c, D. cd
B: ab
Answer: B: ab 
Explanation: None