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
Effective dose in radiation at 2 m, is 1 gray ; At 1 m, it will be 
Select and explain. 
A. 0.25, B. 0.5, C. 2, D. 4
D: 4
Answer: D: 4 
Explanation: None