Question

which pair of undefined terms is used to define a ray? point and line plane and line segment line and plane point and line segment

Explanation:

A ray is defined as a part of a line that starts at a point (called the endpoint) and extends infinitely in one direction. So, the undefined terms used to define a ray are a point (the starting point) and a line (since a ray is a part of a line with a direction).

Answer:

point and line