3. (8 points) As shown in the figure, there are two equal-sized squares, their sides are parallel, and they cover a circle with a radius of 3 cm. The total area of the shaded region is ( ) square cm. ( $\pi$ is taken as 3)
A. 9
B. 10
C. 15
D. 18
【Solution】Solution: As shown in the figure, connect $B D$ and $A C$.
$\because$ Quadrilateral $A B C D$ is a square, $A C=B D=6$,
$$
\therefore S_{\text {shadow }}=S_{\text {circle }}-S_{\text {square } A B C D}=\pi \cdot 3^{2}-\frac{1}{2} \times 6 \times 6=27-18=9 \text {, }
$$

Therefore, the answer is: A.