Triangles
In pyramid only the shape of base changes but the lateral face will be in the shape of triangle

The lateral faces of a pyramid are triangles.

A pyramid is a polyhedron with a polygon base and triangular faces that meet at a common vertex called the apex. The base of the pyramid can be any polygon, such as a triangle, quadrilateral, pentagon, etc. However, the lateral faces of a pyramid are always triangles.

Explanation:

Definition of a Pyramid:
A pyramid is a three-dimensional geometric shape that has a polygonal base and triangular faces that converge at a single point called the apex or vertex. The base can be any polygon, and the number of sides of the base determines the name of the pyramid. For example, a pyramid with a triangular base is called a triangular pyramid or a tetrahedron.

Identification of Lateral Faces:
The lateral faces of a pyramid are the faces other than the base. In other words, they are the triangular faces that connect the apex to the edges of the base. These faces are called lateral faces because they form the sides of the pyramid.

Properties of Lateral Faces:
1. The lateral faces of a pyramid are always triangles. This is because each lateral face is formed by connecting one vertex (the apex) to two vertices of the base, which creates a triangle.
2. The number of lateral faces in a pyramid is equal to the number of sides of the base. For example, a pyramid with a triangular base has three lateral faces, while a pyramid with a square base has four lateral faces.

Example:
Consider a pyramid with a triangular base. The base has three vertices, and the apex is the fourth vertex. To form the lateral faces, we connect each vertex of the base to the apex. These connections create three triangles, which are the lateral faces of the pyramid.

Therefore, the correct answer is option 'A' - the lateral faces of a pyramid are triangles.