Which of the following is most likely to be the subject of study by a geohydrologist

A．Soft, porous rock being worn away by a waterfall.
B．Water depositing minerals on the banks of a gorge through which the water runs.
C．Trapping of water in a sealed underground rock cavern due to an earthquake.
D．Water becoming unfit to drink through the release of pollutants into it from a plant.