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: knowledge of the stars can be used to navigate, Fact2: Navigation is a key element of space travel., Question: What can knowledge of the stars be used for? (A) travel (B) art (C) as a base (D) safety (E) story telling (F) light source (G) vision (H) life
A