Answer: The reaction force is raft pushes back on the person.
Step-by-step explanation:
From Newton's third law, for every action, there is an equal and opposite reaction.
In the given problem, a person pushes against the raft as he dives into the water. As he moves forward but the raft moves backwards in the water.
The action force is his feet against the raft. The reaction force is raft pushing back a person. It causes diver to go forward into the water.