Question

the definition of a circle uses the undefined term
ray
plane
line
arc

Explanation:

A circle is defined as the set of all points in a plane that are at a given distance (radius) from a given point (center). The term "plane" is an undefined term in geometry. A ray is a part - of a line with one endpoint. A line is a straight path that extends infinitely in both directions. An arc is a part of the circumference of a circle. Since the definition of a circle involves the concept of a plane (all points in a plane at a fixed distance from a center point), and "plane" is an undefined term in geometry.

Answer:

plane