This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
Intravenous bolus dose of a new drug produced the changes in blood pressure and hea rate as shown in the graph below. The most probable receptor affinities of this new drug are <img src=" /> 
Select and explain. 
A. a1, a2, b1 and b2, B. a1 and a2, C. b1 and b2, D. Muscarinic M1 and M3
C: b1 and b2
Answer: C: b1 and b2 
Explanation: .