Answer: a.rainwater containing carbon dioxide dissolves underground rock
Explanation:
A sinkhole is also called as cenote, swallet, doline or a depression or hole in the ground that is caused by the collapse of the surface layer.These are also formed due to karst process that involves the dissolution of calcium carbonate from the undersurface rocks or through the suffosion process.
On the basis of the above explanation, a rainwater can also be responsible for the dissolution of the underground rock.
