A coordinate plane with a horizontal line passing through (negative 3, negative 3), (negative 3, 0) and (negative 3, 3). Which is true of the standard form of the equation of the line graphed? The value of A can be –1 if the value of C is 3 and the value of B is 0. The value of A can only be 1, the value of C can only be –3, and the value of B is 0. The standard form of the equation can be shown as 3x = –9. The standard form of the equation can only be x + 3 = 0.