What is the most common way in which sinkholes form?

A) a small explosion of methane gas from coal beds
B) a small explosion of CO₂ gas from dissolving limestone
C) a rising dome of salt finally reaches the surface
D) the roof of a cave collapses

Sinkholes most commonly form when the roof of a cave collapses. This can occur in areas where the rock below the land surface is limestone, carbonate rock, salt beds, or other rocks that can be naturally dissolved by groundwater circulating through them. When the rock dissolves, spaces and caverns develop underground. If the land surface is no longer supported because of the creation of voids beneath, it can suddenly collapse, creating a sinkhole.