You are presented with the quiz "What can convert battery energy into light?"   But you don't know the answer, so you turn to your teacher to ask for hints. He says that "an incandescent light bulb converts electricity into light by sending electricity through a filament" and "additional electricity is stored in the battery".   So, what's the best answer to the question?

Available choices:
(I) incandescent light bulbs
(II) motors
(III) focusing a lens
(IV) an electron lens
(V) generators
(VI) speakers
(VII) hydrogen and oxygen
(VIII) Firecrackers
Answer:
(I)