You will be given a definition of a task first, then some input of the task.
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 greenhouse is used to protect plants by keeping them warm, Fact2: Greenhouse gases act as the glass in a greenhouse., Question: what keeps plants warm? (A) glass (B) trees (C) lipids (D) fats (E) fibers (F) keratin (G) energy (H) heat
Output:
A