When an unbalanced force acts on an object, the change in the object's or depends on the size and direction of the force.
a.
position; mass

b.
direction; mass

c.
mass; speed

d.
speed; direction

The correct answer is "speed and direction".

Explanation:

If the forces acting on the object are balanced then there is no change in the speed of the object and the direction of the object.

If the forces acting on the object are unbalanced then the speed and direction of the object can be changed. If the object is in state of motion or at rest then the state of the object can be changed by applying the external force but it should be unbalanced.

Therefore, when an unbalanced force acts on an object, the change in the object's speed or direction depends on the size and direction of the force.

The correct option is (D).