Question

which defines a circle? two rays with a common endpoint a piece of a line with two endpoints a piece of a line with one endpoint all coplanar points equidistant from a given point

Explanation:

A circle is defined as the set of all points in a plane (coplanar) that are at a fixed distance (equidistant) from a given point called the center. Two rays with a common endpoint form an angle. A piece of a line with two endpoints is a line - segment. A piece of a line with one endpoint is a ray.

Answer:

all coplanar points equidistant from a given point