The correct answer would be choice A).
When the radius of a circle increases, the area does not increase linearly; because the equation for the area is πr², when the radius goes up, the area goes up not by a constant, but by r².
Choices B), C), and D) all describe linear functions; as the side length of a square, the number of gallons of gas purchased, or the time driving increase, the perimeter of the square, the cost of gasoline, and the distance traveled by the car increase at a constant rate.
