18. As shown in Figure 2, Isabella is building a rectangular fort 12 feet long, 10 feet wide, and 5 feet high using cubic bricks with an edge length of 1 foot, and the floor and all four walls are 1 foot thick. Then the total number of bricks needed is ( ).
(A) 204
(B) 280
(C) 320
(D) 340
(E) 600
18. B.

The volume of the fort can be considered as the difference between the volumes of two solid rectangles, then
$$
\begin{array}{l}
V_{\text {outer }}=12 \times 10 \times 5=600, \\
V_{\text {inner }}=10 \times 8 \times 4=320 .
\end{array}
$$

Therefore, a total of $600-320=280$ blocks are needed.