Ans: B
$\begin{array}{cl}
& \dfrac{81^{2n+3}}{(27^{n+1})^2} \\
= & \dfrac{(3^4)^{2n+3}}{(3^3)^{2n+2}} \\
= & \dfrac{3^{8n+12}}{3^{6n+6}} \\
= & 3^{8n+12-6n-6} \\
= & 3^{2n+6}
\end{array}$
