An object is seen to either speed up, slow down, or change direction. these behaviors are caused by what?

A. frictional force

B. stable factors

C. a balanced set of forces

D. unbalanced forces

I believe the correct answer from the choices listed above is option D. An object is seen to either speed up, slow down, or change direction due to unbalanced forces. When a system is subjected to unbalanced forces, the object would tend to move or change in motion. Hope this answers the question.