The answer is:
Forces acting on the sled are paired with equal and opposite forces.
The explanation:
About to push you, this means that he doesn't push yet. If the sled is on level ground and no one is pushing it, then forces are equal and opposite.
The gravity force pulls down and the ground pushes up.
This is Newton's third law:
Newton's third law: If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A.
This law represents a certain symmetry in nature: forces always occur in pairs, and one body cannot exert a force on another without experiencing a force itself.
We can also see Newton’s third law at work by taking a look at how people move about. Consider a swimmer pushing off from the side of a pool.
