What is the definition of a adverb? (this is for my brother)

Why did orson welles change the beginning of the war of the worlds for his radio broadcast? a. to capture the attention of his listeners, who may have been doing other things b. to get around copyright laws associated with using material from a published book c. to ask members of the audience to call family and friends and encourage them to listen d. to remind listeners to call police for more information