This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2019, Subject name: Microbiology
[{'content': 'Koplik spots are seen in? \nSelect and explain. \nA. Mumps, B. Measles, C. Rubella, D. Varicella', 'role': 'user'}, {'content': "Answer: B \nExplanation: Koplik's Spots: They are pathognomonic of measles. Their presence establishes the diagnosis of measles. These are bluish grey specks on grain substance on a red base which usually appear on the buccal mucosa opposite the second molar. They appear at the end of the prodrome, just before the appearance of the rash. Koplik's spots usually appear after 2 days of illness and last for 24-48 hours. May also appear on the mucous membrane of the conjunctiva and the vagina.", 'role': 'assistant'}]