计算下列极限.
(1) $\lim \limits_ {n \rightarrow \infty }(1 2^{n} 3^{n})^{ \frac {1}{n}}$.
(2) $\lim \limits_ {n \rightarrow \infty } \left ( \dfrac {1}{4n^{2} 1} \dfrac {2}{4n^{2} 2} \cdots \dfrac {n}{4n^{2} n} \right )$.
$\text{A.}$
$\text{B.}$
$\text{C.}$
$\text{D.}$