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: Medicine
The 'a' wave of jugular venous pulse is produced by- 
Select and explain. 
A. Atrial relaxation, B. Atrial systole, C. Atrial diastole, D. Rapid venous filling
B: Atrial systole
Answer: B: Atrial systole 
Explanation: None