A19-year-old woman has painful ulcers on the labial mucosa and buccal mucosa of 4 days duration. she has had similar ulcers on previous occasions, and each time the lesions healed in approximately 7 days. the best diagnosis is

The best diagnosis is aphthous ulcers.
The description above is fits what aphthous ulcers are. They might occur several times a year, and always last about 7 days total. These are painful ulcers which may appear in a person's mouth a couple of times a year and are a minor nuisance. 

Based on the age and demographic, the best diagnosis given the facts is genital herpes. The recurrence of the ulcers in the labial region are indicative of a chronic viral infection. The odds of genital herpes from a single unprotected exposure are quite realistic at approximately 1 in 1000 which support assertion that herpes is the best diagnosis.

The answer is c hope this