问题
下面【常见数列的前 $n$ 项和】中，正确的是哪个？选项
[A]. $1^{2} + 2^{2} +$ $3^{2} + \cdots + n^{2} =$ $\frac{1}{6} \cdot $ $n \cdot (n – 1) \cdot (2n – 1)$[B]. $1^{2} + 2^{2} +$ $3^{2} + \cdots + n^{2} =$ $\frac{1}{6} \cdot $ $n \cdot (n + 1) \cdot (2n – 1)$
[C]. $1^{2} + 2^{2} +$ $3^{2} + \cdots + n^{2} =$ $\frac{1}{6} \cdot $ $n \cdot (n + 1) \cdot (2n + 1)$
[D]. $1^{2} + 2^{2} +$ $3^{2} + \cdots + n^{2} =$ $\frac{1}{6} \cdot $ $(n + 1) \cdot (2n + 1)$
$1^{2} + 2^{2} +$ $3^{2} + \cdots + n^{2} =$ $\frac{1}{6} \cdot $ $n \cdot (n + 1) \cdot (2n + 1)$