Definition: 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: glass cause refraction of light, Fact2: Prisms are round pieces of glass., Question: What do prisms do to light? (A) focusing a lens (B) Refract it (C) Reflect it (D) protect them (E) Absorb it (F) observe it (G) It expands (H) Diffraction
Output:
B