4. Among all the triangles formed by any 3 of the 8 vertices of a rectangular cuboid, the number of acute triangles is
A. 0
B. 6
C. 8
D. 24
Among the 8 vertices of a cuboid, the triangle formed by 3 vertices is only an acute triangle when the three edges starting from the same vertex are used. Therefore, there are 8 acute triangles in total. So the answer is $C$.