3. For a regular triangle, a square, and a regular hexagon with the same perimeter, their areas are $S_{3}, S_{4}, S_{6}$ respectively, then
(A) $S_{3}>S_{4}>S_{6}$;
(B) $S_{6}>S_{4}>S_{3}$;
(C) $S_{6}>S_{3}>S_{4}$;
(D) $S_{3}>S_{6}>S_{4}$;
(E) $S_{4}>S_{6}>S_{3}$.
3. (B)

Let the same perimeter be $12 l(l>0)$, then their areas are
$$
\begin{array}{l}
S_{3}=\frac{1}{2} \times 4 l \times 4 l \times \sin 60^{\circ}=4 \sqrt{3} l^{2}, \\
S_{4}=3 l \times 3 l=9 l^{2}, \\
S_{6}=6 \sqrt{3} l^{2} . \\
\therefore \quad S_{6}>S_{4}>S_{3} .
\end{array}
$$