In the Diagram Below, the Importance of the Falling Precipitation

Multiple Choice

In the diagram below, the importance of the falling precipitation at "A" for the global carbon cycle is that

A) the falling rain makes carbon in the atmosphere more inert - giving it much greater potential to act as a greenhouse gas and warm the Earth.
B) the falling rain brings CaCO₃ which was trapped in the atmosphere to the surface, cooling the Earth.
C) the falling rain lubricates the Earth's surface, making crustal deformation more likely, which would bring carbon stored in the lithosphere back up to the atmosphere, warming the Earth.
D) CO₂ combines with water to form H₂CO₃, removing carbon from the atmosphere and cooling the Earth.