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: Carbon may be stored in sedimentary rock for millions of years., Fact2: Limestone is a rock composed of calcium, carbon and oxygen., Question: what is in limestone? (A) abrasion (B) fossils (C) an anion (D) acid (E) nitrogen (F) gypsum (G) carbon (H) NaCl
G