4. As shown in Figure 1, there are three regular hexagons with side lengths increasing in sequence. Based on the existing hexagonal lattice, an additional layer is added to form the point lattice within the next layer of the hexagon. Then, the fourth layer of the hexagon contains ( ) points.
(A) 35
(B) 37
(C) 39
(D) 43
(E) 49
4. B.

Let the $n$-th hexagon contain $h_{n}$ points. Then
$$
\begin{array}{l}
h_{1}=1, \\
h_{n}=h_{n-1}+6(n-1)\left(n \in \mathbf{Z}_{+}, n \geqslant 2\right) .
\end{array}
$$

Thus, $h_{2}=1+6=7$,
$$
\begin{array}{l}
h_{3}=7+12=19, \\
h_{4}=19+18=37 .
\end{array}
$$