Impulsive, emotional Romeo acts as a character foil for Paris, who is stable yet dull. Option D is the right one.
Whe refering to literature, the term foil makes reference to a character who contrasts with other characters, often their qualities are quite the opposite from those of other characters.
Paris in the play Rome and Juliet is a suitor of Juliet. He is described as a handsome, wealthy man and a kinsman to Prince Escalus.
