Sinkholes can form when
a. rainwater containing carbon dioxide dissolves underground rock
b. streams drop sediment as they enter lakes
c. the water table rises due to flooding
d. minerals dripping from a cavern ceiling form stone pendants

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.