A tetrahedron is a pyramid whose base is a:

Options

A. triangle
B. square
C. rectangle
D. quadrilateral

Answer

To solve the question "A tetrahedron is a pyramid whose base is a:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of a Tetrahedron**:
A tetrahedron is a type of pyramid that has four triangular faces. It is one of the simplest three-dimensional shapes.

2. **Identify the Options**:
The options provided are:
- Option A: Triangle
- Option B: Square
- Option C: Rectangle
- Option D: Quadrilateral

3. **Visualize the Tetrahedron**:
To better understand the shape, we can visualize or draw a tetrahedron. It consists of four vertices, six edges, and four triangular faces.

4. **Determine the Base of the Tetrahedron**:
In a tetrahedron, one of the triangular faces acts as the base. Since all faces are triangles, the base must also be a triangle.

5. **Select the Correct Option**:
Based on our understanding, the base of a tetrahedron is a triangle. Thus, the correct answer is:
- Option A: Triangle

### Final Answer:
The base of a tetrahedron pyramid is a triangle.

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