Joe claims that the equation , where b is a real number, represents the graph of a straight line. Which statement BEST classifies Joe's claim? A. Joe's claim is true only when b is 0. B. Joe's claim is true for all values of b. C. Joe's claim is not true for any value of b. D. Joe's claim is true only when b is not zero.

D. Joe's claim is true only when b is not zero.