What is the justification for the first step in proving the formula for factoring the sum of cubes?
A^3+b^3=(a+b)(a^2-ab+b^2)

=a^3a^2b+ab^2+a^2b+ab^2+b^3

A) distributive property
B) commutative property
C) definition of additive inverse
D) definition of mulitiplicative inverse