The correct answer is: Rain water.
Rainwater is diffused into the ground by gravitational force. When rain falls, it hits the ground and starts to soak into the soil. The water then moves through the soil and into the groundwater. The groundwater is the water that is stored underground in aquifers.
Ocean water is not diffused into the ground by gravitational force. Ocean water is salty and has a high density. This means that it is heavier than freshwater and does not sink into the ground. Instead, ocean water stays on the surface of the Earth and forms oceans.
River water is also not diffused into the ground by gravitational force. River water is freshwater that flows through rivers. The water in rivers is constantly moving and does not have time to soak into the ground. Instead, the water in rivers flows into oceans or lakes.
Therefore, the correct answer is: Rain water.