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
(C)
4. 【Analysis and Solution】The number of triangles formed by any 3 of the 8 vertices of a rectangular prism is $\mathrm{C}_{8}^{3}$, and these triangles can only be right triangles or acute triangles. There are 6 right triangles for each vertex of the rectangular prism when it serves as the right-angle vertex, so there are a total of $6 \times 8=48$ right triangles among the $\mathrm{C}_{8}^{3}$ triangles. Therefore, the number of acute triangles is $\mathrm{C}_{8}^{3}-48$ $=8$.