What is the name of the point that you use to define a parabola?A.FocusB.DirectrixC.VertexD.Center

The point that is commonly used to define a parabola is called the Focus.

Explanation:

1. A parabola is defined as the set of all points that are equidistant from a fixed point (the focus) and a fixed line (the directrix).
2. The Focus is the specific point inside the parabola where the parabola curves towards, and it plays a significant role in the geometric definition of the shape.
3. The Directrix is the line which, along with the focus, helps to define the parabola, but it is not a point.
4. The Vertex is the point where the parabola changes direction, located midway between the focus and the directrix.
5. The Center is typically associated with circles or ellipses, not parabolas.

Thus, the correct answer is A. Focus.