what is the difference? x/x^2-2x-15 -4/x^2+2x-35 '
a. x^2+3x+12/(x-3(x-5)(x+7)
b. x(x+3-12)/(x+3)(x-5)(x+7)
c. x^2+3x+12/(x+3)(x-5)(x+7)
d. x^2+3x-12/(x+3)(x-5)(x+7)