With respect to a fixed point, motion is defined as a change in-

A)speed
B)position

With respect to a fixed point, motion is defined as a change in position.

Explanation:

MOTION -:  Motion is described as the fact in which any object or body changes its position over the time with respect to a fixed point .

Motion is defined as displacement, distance, velocity , acceleration, speed , and time in mathematical terms. By linking an observer to a frame of reference and measuring the shift in the position of the body with a change in time relative to that frame, the motion of a body is observed.      

i think that the answer is c