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
Glucagon is most effective for which of the following conditions ? 
Select and explain. 
A. Cocaine intake with BP of 180/110 mmHg, B. Old man with decreased BP/decreased heart rate due to atenolol, C. Old man with type 2 diabetes mellitus and no glipizide for 4 days, D. Female with lactic acidosis due to shock
B: Old man with decreased BP/decreased heart rate due to atenolol
Answer: B: Old man with decreased BP/decreased heart rate due to atenolol 
Explanation: None