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: energy is used for heating a building by a heating system, Fact2: Passive solar thermal energy involves heating buildings using direct sunlight., Question: A method of heating a building might be what? (A) dangerous (B) Blizzards (C) Heated arguments (D) threatened (E) major threat to health (F) Direct sunlight. (G) Mothballs (H) slow and inefficient
F