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
First sign after radiation R,, is: 
Select and explain. 
A. Erythema, B. Necrosis, C. Burns, D. Deep ulcer
A: Erythema
Answer: A: Erythema 
Explanation: Ans. Erythema