Ans: C
$\begin{array}{cl}
& (a-b)(a^2 +ab – b^2) \\
= & a^3 +a^2b -ab^2 -a^2b – ab^2 +b^3 \\
= & a^2 – 2ab^2 +b^3
\end{array}$
$\begin{array}{cl}
& (a-b)(a^2 +ab – b^2) \\
= & a^3 +a^2b -ab^2 -a^2b – ab^2 +b^3 \\
= & a^2 – 2ab^2 +b^3
\end{array}$
