A student needs to make a circular cardboard piece with an area between 154 square inches and 616 square inches. The function f(r) relates the area of the cardboard piece, in square inches, to the radius r in inches. Which of the following shows a reasonable domain for f(r)?
A) 7 < r < 14
B)154 < r < 616
C) all positive integers less than 7
D) all positive integers between 14 and 154