Given the task definition and input, reply with output. In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: a cavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone, Fact2: Any time water and carbon dioxide mix, carbonic acid is the result., Question: Which of the following added to groundwater creates caverns? (A) a solute (B) permineralization (C) calcite (D) storing water (E) flooding (F) salinity (G) carbon dioxide (H) heating liquids
G