When subtracting a polynomial Q(x) from another polynomial P(x), which one of the following steps is performed on Q(x) before combining like terms?
a) Add Q(x) to P(x) without any change
b) Replace every coefficient of Q(x) by its absolute value and then add
c) Multiply each term of Q(x) by 2 and then add
d) Change the sign of every term of Q(x) and then add it to P(x)