This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
[{'content': "In measles, when do the Koplik's spots appear? \nSelect and explain. \nA. On the day that fever occurs, B. On the day that rashes appear, C. 1 -3 days before the rashes appear, D. 1-2 days before the fever occurs", 'role': 'user'}, {'content': "Answer: C \nExplanation: In measles ,a prodromal illness,1-3 days before the rash,occurs ,with upper respiratory symptoms ,conjunctivitis , & the presence of the pathognomonic Koplik's spots,small white spots surrounded by erythema on the buccal mucosa. Reference: Harrison20th edition pg 879", 'role': 'assistant'}]