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: Physiology
S.A. node acts as a pacemaker of the hea because of the fact that it: 
Select and explain. 
A. Is capable of generating impulses spontaneously, B. Has rich sympathetic innervations., C. Has poor cholinergic innervations, D. Generates impulses at the highest rate.
D: Generates impulses at the highest rate.
Answer: D: Generates impulses at the highest rate. 
Explanation: D i.e. Generates impulses at the highest rate