The correct response is:
A. When the octopus ejects the water out, the water applies an equal force on the octopus in the opposite direction.
This illustrates Newton's Third Law, which states that for every action, there is an equal and opposite reaction. When the octopus pushes water out, it exerts a force on the water, and in turn, the water exerts an equal force back on the octopus, propelling it in the opposite direction.