Write the equation of the circle centered at (4,-9) with a diameter of 18. Which of the following options correctly represents the equation of the circle?

A) (x-4)² + (y+9)² = 9
B) (x-4)² + (y+9)² = 18
C) (x+4)² + (y-9)² = 9
D) (x+4)² + (y-9)² = 18