23. Given that the perimeter of an equilateral triangle and a regular hexagon are the same. If the area of the equilateral triangle is 4, then the area of the regular hexagon is ( ).
(A) 4
(B) 5
(C) 6
(D) $4 \sqrt{3}$
(E) $6 \sqrt{3}$
23. C.

Let the side length of the equilateral triangle be $a$. Then the side length of the regular hexagon is $\frac{a}{2}$.
From the problem, we know
$$
\frac{\sqrt{3}}{4} a^{2}=4 \Rightarrow a^{2}=\frac{16}{\sqrt{3}} \text {. }
$$

Therefore, the area of the regular hexagon is
$$
\frac{3 \sqrt{3}}{2}\left(\frac{a}{2}\right)^{2}=\frac{3 \sqrt{3}}{8} a^{2}=6 .
$$