Newton’s first law states that if an objects velocity is changing a must be acting on it.
a) force
b) mass
c) acceleration
d) inertia

(a)

Explanation Newtons First Law can be written as the formula

since acceleration is the changing of velocity as its formula is

Thus, a force must be acting on an accelerating/decelerating object

It is not mass as the mass does not act on the object but rather the mass is acting on the surface of the ground.Changing velocity is already acceleration inertia is the term used to describe Newtons first law

Gravity, from the center of mass of the box, extending downward normal force, from the floor under the box, extending upward, equal to gravity push force, acting at a point on the box, extending in the direction of motion friction, acting at any point on the box directly opposite the push, extending directly opposite to the motion