3. In the spatial rectangular coordinate system, given $O(0,0,0), A(1,0,0), B(0,1,0), C(0,0,1)$, the number of points that are equidistant from the planes $O A B$, $O B C$, $O A C$, and $A B C$ is ( )
A: 1
B: 4
C: 5
D: infinitely many
Huijun $\mathrm{C}$.
Analysis The incenter of the tetrahedron $O A B C$ and the centers of the four "exspheres" are equidistant from the faces $O A B$, $O B C$, $O A C$, and $A B C$, so the number of points that satisfy the condition is 5.