答案：D
$\begin{array}{cl}
& (x+1)(x^2 + x +1) \\
= & x^3 + x^2 + x + x^2 + x + 1 \\
= & x^3 +2x^2 + 2x + 1
\end{array}$
$\begin{array}{cl}
& (x+1)(x^2 + x +1) \\
= & x^3 + x^2 + x + x^2 + x + 1 \\
= & x^3 +2x^2 + 2x + 1
\end{array}$
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