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: matter vibrating can cause sound, Fact2: All guitars produce sound through the mechanical vibration of strings., Question: What do guitar strings do? (A) Charge the guitar (B) Relieve pain (C) Vibrates (D) reproduce (E) squeeze (F) Bend (G) Create silence (H) Mute the guitar
C