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: Feathers help birds fly and provide insulation., Fact2: To survive the chill, warm-blooded penguins rely on feathers and fat for insulation., Question: Birds do what using the feathers that help them to fly? (A) to move people (B) running and lifting (C) survive the chill (D) during the day (E) Move to another area (F) Earth orbiting the Sun (G) to stay warm (H) supersonic
C