SolUtion
D

A tetrahedron has four corners (or vertices). When a corner is removed, three new vertices are formed. Therefore the number of vertices the remaining shape will have is $4 \times 3=12$.
1. Julio cuts off the four corners, or vertices, of a regular tetrahedron, as shown.
How many vertices does the remaining shape have?
A 8
B 9
C 11
D 12
E 15