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: Radiology
At t = 0 there are 6 x 1023 radioactive atoms of a substance, which decay with a disintegration constant (A,) equal to 0.01/sec. What would be the initial decay rate? 
Select and explain. 
A. 6 x 1023, B. 6 x 1022, C. 6 x 1021, D. 6 x 1021
C: 6 x 1021
Answer: C: 6 x 1021 
Explanation: Ans. 6 x 1021