7. A tetrahedron is a solid figure which has four faces, all of which are triangles.
What is the product of the number of edges and the number of vertices of the tetrahedron?
A 8
B 10
C 12
D 18
E 24
7. E The tetrahedron has 6 edges and 4 vertices, so the required product is $6 \times 4=24$.