Question

which best describes a reference frame?
○ a distance over which an object moves
○ the difference between start and end velocity
○ a position from which something is observed
○ the average speed of a group of objects

Explanation:

A reference frame is a coordinate system used to observe the position and motion of objects. The option "a position from which something is observed" matches the definition of a reference frame, as it's the perspective or position for observing. The other options describe distance, velocity difference, or average speed, not a reference frame.

Answer:

a position from which something is observed