In "Racing the Storm", the character that is a foil to Keri is the waiter. Option D is correct.
A foil is a character that shows traits that oppose the traits of another character, such as the protagonist. The characteristics of both characters are opposite and they are expressed by the way in which both characters act and speak. This opposition is employed in order to highlight the traits of the characters.
Racing the Storm exposes the stories and implications of the vexing experiences of poor people of color in New Orleans.