3. The tetrahedron S-ABC is empty, with three pairs of edges being equal, sequentially $\sqrt{34}, \sqrt{41}, 5$. Then the volume of the tetrahedron is ( ).
(A) 20
(B) $10 \sqrt{7}$
(C) $20 \sqrt{3}$
(D) 30
3. A.

As shown in Figure 1, complete the rectangular prism, and let its length, width, and height be $x$, $y$, and $z$ respectively. Then we have
$$
\left\{\begin{array}{l}
x^{2}+y^{2}=5^{2}, \quad A \\
y^{2}+z^{2}=(\sqrt{41})^{2}, \\
z^{2}+x^{2}=(\sqrt{34})^{2} .
\end{array}\right.
$$

Solving, we get $x=3, y=4, z=5$.
$$
\therefore V_{S-A B C}=\frac{1}{3} V_{\text {prism}}=\frac{1}{3} \times 3 \times 4 \times 5=20 \text {. }
$$