3. In the tetrahedron $S-ABC$, the three pairs of opposite edges are equal, and are $5$, $4$, and $x$ respectively. Then the range of values for $x$ is ( ).
(A) $(2, \sqrt{41})$
(B) $(3,9)$
(C) $(3, \sqrt{41})$
(D) $(2,9)$
3. C.

A tetrahedron can be embedded in a rectangular prism, in which case the three pairs of opposite edges of the tetrahedron are the face diagonals of the rectangular prism. Therefore, 5, 4, and $x$ are the side lengths of an acute triangle.
Thus, $x \in\left(\sqrt{5^{2}-4^{2}}, \sqrt{5^{2}+4^{2}}\right)$, which means $x \in(3, \sqrt{41})$.