A1. From a pyramid with a base edge length of $5 \mathrm{~cm}$, we cut off all five vertices such that all edges of the small pyramids that have been cut off are shorter than $1 \mathrm{~cm}$. Which of the following polygons is not a face of the resulting solid?
(A) triangle
(B) quadrilateral
(C) pentagon
(D) hexagon
(E) octagon

![](https://cdn.mathpix.com/cropped/2024_06_07_58dcb28c79ea4cc315e1g-02.jpg?height=323&width=446&top_left_y=878&top_left_x=1459)
A1. The side surface that was previously the base of the pyramid is now an octagon. The surfaces that were previously the side surfaces of the pyramid are now hexagons. At the vertex that was previously the apex of the pyramid, a surface that is a quadrilateral is formed, and at the other vertices of the pyramid, surfaces that are triangles are formed. None of the side surfaces of the resulting solid are pentagons.