The correct answer is C) a revolution. A celestial body's complete orbit around another body, such as a planet orbiting the Sun or a moon orbiting a planet, is known as a revolution. This is because the celestial body completes a full, cyclical movement around the object it is orbiting. The other options are incorrect: A) Rotation refers to the spinning motion of a celestial body on its own axis, not its orbit around another body. B) Nutation is a small, periodic shift in the orientation of a celestial body's axis of rotation, not its overall orbital path. D) Space motion is a more general term that can encompass both rotational and orbital movements, but does not specifically describe a complete orbit or revolution around another body.