which part of an objects rate of change best defines acceleration?\no velocity\no speed\no position\no force

Brief Explanations:

Acceleration is defined as the rate of change of velocity. It takes into account both the magnitude (speed - part of velocity) and direction of motion. Speed is just the magnitude of velocity, position change gives velocity, and force causes acceleration according to Newton's second law but is not the definition of acceleration itself.

Answer:

A. velocity