The correct answer is "Absorption of rainfall by soil."
The hyrdosphere refers to all water on the earth's surface. The geosphere, in this context, refers to the solid parts of the earth (rocks, sand, etc.) Since rain is part of the hydrosphere and soil is part of the geosphere, rain soaking into the soil would be an interaction between the two. The other choices deal with changes in the hyrdrosphere, but there is no interaction with the geosphere.
