In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").
Q: Science fact: a cavern is formed by carbonic acid in groundwater seeping through rock and dissolving (A) sedimentary rock which is  composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs, (B) metamorphic rocks that are formed under the surface of the earth from the metamorphosis, (C) igneous rocks which are formed when magma  cools and hardens or (D) artist who play the music genre called rock and roll.
A: 
A