Pathognomic clinical feature of measles are -

Ans. is 'b' i.e., Kolpik spots * Koplik's spots are pathognomonic of measles and consist of bluish white dots ~1 mm in diameter surrounded by erythema. The lesions appear first on the buccal mucosa opposite the lower molars but rapidly increase in number to involve the entire buccal mucosa. They fade with the onset of rash.