Acceleration of a particle is non-zero whenA     direction of velocity changes B     magnitude of velocity changesC     either of aboveD     speed is constant

The acceleration of a particle is non-zero when either the direction of velocity changes or the magnitude of velocity changes. Therefore, the correct answer is C - either of the above.

Here's why:

Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. Acceleration is the final velocity minus the initial velocity per time, with a direction.

A. If the direction of velocity changes, even if the object is moving at a constant speed, it is accelerating because its direction is changing.

B. If the magnitude of velocity changes, it means the speed of the object is changing, which is also a form of acceleration.

D. If the speed is constant and the direction is not changing, then the acceleration is zero.

So, the correct answer is C. Either the direction or the magnitude of velocity changes.