We have congruent equilateral triangles. What do we need more to make a pyramid?
A square with same side length as of triangle.
Explanation for correct option:
Option B: A square with same side length as of triangle.
Pyramid: A pyramid is a three dimensional shape. A pyramid has a polygonal base and flat triangular faces, which join at a common point called the apex. A pyramid is formed by connecting the bases to an apex. Each edge of the base is connected to the apex, and forms the triangular face, called the lateral face.
Now, we have congruent equilateral triangles, it means we required only one base which has sides to connect with congruent equilateral triangles.
Therefore, we required a square with the same length as of triangle to exactly connect with the congruent equilateral triangles.
Hence, option (B) is correct answer.