This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ECG and Arrhythmia 2, Subject name: Medicine
A 40 year old man was admitted to the hospital emergency with sudden onset of the symptoms and signs of severe left ventricular failure. Calculate the atrial rate of the patient. 
Select and explain. 
A. 100/min, B. 150/min, C. 200/min, D. 300/min
D: 300/min
Answer: D: 300/min 
Explanation: Ventricular rate : 1500/10 = 150 ECG shows HR of 150/min with normal axis. Saw tooth waves are noted with 2:1 AV block. Ventricular rate is 150/min therefore the atrial rate would be 300/min.