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
A most common cause of erythema multiforme – 
Select and explain. 
A. Herpes simplex, B. DM, C. Pityriasis rosae, D. Erysipelas
A: Herpes simplex
Answer: A: Herpes simplex 
Explanation: Most of the cases of erythema multiforme are idiopathic, but amongst the known causes, HSV is the most important cause.