Fact 1: Acavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone. Fact 2: Erosion by acid solutions is only one way that caves form. Given the two facts above, answer the question "how are caves formed?" with the following options: - less water - eruptions - Water expanding - storing water - volcanoes - by humans - chemical erosion - hard outer covering
A:
chemical erosion