4. If a regular hexagon $T_{1}$ is inscribed in $\odot O$, and a regular hexagon $T_{2}$ is circumscribed about $\odot O$, then the ratio of the area of $T_{1}$ to the area of $T_{2}$ is ( ).
(A) $2: 3$
(B) $3: 4$
(C) $4: 5$
(D) $5: 6$
4.B.

As shown in Figure 3, $T_{1}$ and $T_{2}$ are respectively divided into isosceles triangles with a vertex angle of $120^{\circ}$. Then, $T_{1}$ contains 18 isosceles triangles, and $T_{2}$ contains 24 isosceles triangles, with the ratio being $18: 24=3: 4$.