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: Anatomy
Autonomic supply to S.A node is - 
Select and explain. 
A. Parasympathetic excitatory, B. Sympathetic excitatory, C. Both excitatory, D. Both inhibitory
B: Sympathetic excitatory
Answer: B: Sympathetic excitatory 
Explanation: Sympathetic supply to heart excites the cardiac activity to increase the heart rate and contractility.