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: a compass is used for determining direction, Fact2: Compass needles line up with magnetic fields., Question: What is used for determining direction? (A) chemical messengers (B) speedometers (C) thermometers (D) barometric pressure (E) trees and flowers (F) magnetic fields (G) lamphreys (H) feedback mechanisms
F