13. As shown in Figure 2, given that a regular hexagon with a side length of 1 is surrounded by six congruent regular hexagons. Then the area of $\triangle A B C$ is ( ).
(A) $2 \sqrt{3}$
(B) $3 \sqrt{3}$
(C) $1+3 \sqrt{2}$
(D) $2+2 \sqrt{3}$
(E) $3+2 \sqrt{3}$
13. B.

By symmetry, we know that $\triangle ABC$ is an equilateral triangle. Therefore,
$$
S_{\triangle ABC}=\frac{\sqrt{3}}{4} AB^{2}=\frac{\sqrt{3}}{4}\left(4 \sin 60^{\circ}\right)^{2}=3 \sqrt{3} .
$$