Definition: 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").
Input: Fact1: radioactive dating is used to determine the age of fossils, Fact2: Radioactive isotopes are commonly used for dating ., Question: what is used to determine the age of fossils? (A) Conifers (B) Sediment (C) calcite (D) skull (E) loose soil (F) cracking (G) exoskeleton (H) isotopes
Output:
H