an adjective is a descriptive word, it describes a noun, which is a 'name' word (i.e: the name of an item, the name of a place; e.g: shoes are the name of the things you wear on your feet, 'shoe's' are the noun)
the 'descriptive' word, the adjective, is something which tells you more about the noun.
therefore, the answer should be: a) with the pink spots; modifies butterfly
because 'with the pink spots' describes the noun, the 'butterfly'.
