3. Let the base edge length of the regular tetrahedron $S-ABC$ be 3, and the side edge length be 2. Then the angle formed by the side edge $SA$ and the base $ABC$ is ( ).
(A) $30^{\circ}$
(B) $45^{\circ}$
(C) $60^{\circ}$
(D) $\arctan \sqrt{2}$
3. A.

Let the projection of vertex $S$ on the base $\triangle A B C$ be $H$. Then $H$ is the circumcenter of $\triangle A B C$.
Thus, $A H=\frac{2}{3} \times 3 \times \frac{\sqrt{3}}{2}=\sqrt{3}$.
Therefore, $\angle S A H=30^{\circ}$.