For which one of the following rational functions can all unknown constants be obtained merely by substituting the zeros of its denominator after writing its partial–fraction form?
a) (x−1)(x2+4)5x+7
b) (x+1)(x−2)24x−3
c) (x−2)(x+3)(x+5)3x+2
d) x(x2+9)x2+1