Q: Fact 1: Acavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone. Fact 2: Carbon dioxide dissolved in rainwater forms carbonic acid. Given the two facts above, what chemical creates a cavern?

Options:
(a). carbonic acid.
(b). heating liquids.
(c). hydrogen and oxygen.
(d). aqueous solution.
(e). salt.
(f). oxygen.
(g). hydrogen.
(h). flow of electrons.
A:
(a).