Infiltration is the process by which rainwater becomes
a. ocean water.
b. groundwater.
c. saltwater.
d. river water.

Infiltration is the process by which rainwater becomes ground water. So it's B. The rainwater that falls on the surface of the earth or soil slowly gets absorbed by the soil. This process is called infiltration. The water from outside is infiltrating the ground and mixing with the water that is already present under the ground. It helps to soften and moist the soil of the earth very quickly and the farmers take the advantage of sowing seeds of variety of plants.