Sinkholes are formed by precipitation, and natural openings on the surface that lead to caves are called sinkholes, or swallow holes. Given these facts, natural openings on the surface, leading to caves are formed by what among the following options:
- hydrogen and oxygen
 - aqueous solution
 - precipitation
 - calcite
 - erosion
 - flow of electrons
 - Calcium carbonate
 - Physical weathering


 

   precipitation      