Fact 1: Acavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone.

Fact 2: When carbon dioxide is in water, it creates carbonic acid.

Given the two facts above, answer the question "What forms caverns by seeping through rock and dissolving limestone?" with the following options: 
- pure oxygen
 - Something with a head, thorax, and abdomen
 - basic building blocks of life
 - carbon dioxide in groundwater
 - magma in groundwater
 - oxygen in groundwater
 - At the peak of a mountain
 - underground systems


 

    carbon dioxide in groundwater     