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: a switch is used to start the flow of current in an electrical circuit, Fact2: With switch closed, electricity flows through wires, switch and bulb, to light up the bulb., Question: What powers a light bulb? (A) structure and function (B) The tungsten filament (C) photosynthetic pigments? (D) Unplugging a lamp (E) heat production (F) heat is produced (G) Unscrewing a light bulb (H) The flow of electrical current
H