Instructions: 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").
Input: Fact1: a black hole is formed by a high-mass star collapses, Fact2: Then, gravity collapses the star., Question: What is the initial cause of black holes? (A) energy (B) gravity (C) heat (D) photons (E) mechanical (F) sun's heat (G) cracking (H) Smoking
Output:
B