Which of the following statements is true about completing a square? A. When completing the square, subtract the square of half the coefficient of x from both sides of the equation. B. When completing the square, add the square of half the coefficient of x to only the x^2+bx side of the equation. C. When completing the square, add half the coefficient of x to both sides of the equation. D. When completing the square, add the square of half the coefficient of x to both sides of the equation.