Final answer:
Decreasing the mass of the box will not make it start moving down the incline because it proportionally decreases the normal force and frictional force, and by itself does not affect the likelihood of the box starting to slide down the slope. Hence, the correct answer is option (d).
Step-by-step explanation:
The action that will definitely not make the box start moving down the incline is decreasing the mass of the box. When considering the factors that could cause a box to start moving down an incline, we look at forces such as gravity, friction, and any applied forces. Increasing the incline angle would typically make it more likely for the box to move, as it would increase the component of gravitational force acting down the slope. Reducing the coefficient of friction also makes it more likely for the box to slide, as there would be less resistance opposing the motion.
Increasing the applied force parallel to the incline would add to the forces pushing the box downslope, potentially overcoming static friction. However, decreasing the mass of the box does not directly affect the likelihood of the box starting to move down the slope as it decreases both the normal force and the frictional force proportionally, assuming all other factors are kept constant.