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: Dental
Recurrent oral ulcers with pain and erythematous halo around them, diagnosis is – 
Select and explain. 
A. Apthous ulcer, B. Herpes, C. Chicken pox, D. Measels
A: Apthous ulcer
Answer: A: Apthous ulcer 
Explanation: Recurrent oral ulcers with erythematous halos suggest the diagnosis of Aphthous ulcer.