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").
Example: Fact1: a plant requires sunlight to grow, Fact2: Plants to avoid are fast-growing vines that can take over an area in no time., Question: What requires sunlight in order to take over an area? (A) spores (B) fish (C) plants (D) humans (E) pods (F) Oak (G) opossums (H) coral
Example solution: C
Example explanation: This is a good example. Based on the facts plants require sunlight in order to take over an area.

Problem: 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
Solution: G