How does a sinkhole form?

A. Carbonic acid eats away at an underground limestone formation and eventually creates a depression when the ground surface collapses.
B. Sulfuric acid eats away at an underground limestone formation and eventually creates a depression when the ground surface collapses.
C. Groundwater under pressure pushes upward on a layer of soil at the surface, eroding it from beneath until it collapses.
D. Groundwater heated to boiling temperatures by geothermal energy forms bubbles of steam that push up on surface rock until it collapses.