A boy is pushing forward on a crate with a force of 100 newtons. The reaction force is the crate pushing back on the boy with a force of 100 newtons. the crate moving forward at a constant rate. the crate remaining at rest with a weight of 100 newtons. the crate accelerating 10 m/s2 forward.
This is somewhat confusing, but I'd have to go with A. Since Newton's Third Law states that every action has an equal but opposite reaction.