Ans: D
The height of the lateral face
$\begin{array}{cl}
= & \sqrt{12^2 + (\dfrac{18}{2})^2 } \\
= & 15 \text{ cm}
\end{array}$
Therefore, the total surface area of the pyramid
$\begin{array}{cl}
= & 18 \times 18 + 4 \times \dfrac{1}{2} \times 18 \times 15 \\
= & 864\text{ cm}^2
\end{array}$
