Final answer:
The interaction in question is between the biosphere and geosphere, where plants in the biosphere help soil in the geosphere retain moisture by controlling evaporation. This process is delicate but critical for maintaining an equilibrium in the ecosystem.
Step-by-step explanation:
In the context of the question, when discussing how plants help soil remain moist by helping to control evaporation, we're looking at the interaction between different spheres of Earth's ecosystem. Specifically, the interaction is between the biosphere and the geosphere. Plants, as part of the biosphere, use water from the soil (geosphere) to facilitate photosynthesis and life processes. They reduce water loss from the soil by providing shade and also by a process known as transpiration, which is the evaporation of water from plant leaves. As plants transpire, they release water vapor back into the atmosphere, helping to modulate temperature and climate, a process which is intrinsically linked to the hydrosphere. However, the dominant interaction described by the soil moisture retention is C) Geosphere and biosphere.
Plants (biosphere) retain soil moisture and control evaporation through their biological processes, specifically transpiration, thus interacting predominantly with the geosphere by minimizing water loss and modifying the local climate.