A long-lasting filament.
Option: C
Explanation:
Thomas Edison wasn't the one who invented the bulb; rather he was the one whose mind enhanced the previous inventions on the light bulb and converted into the electric bulb officially. In 1878, he filed a patent application on improving the electric lights. He took a thin filament that possessed high electric resistance and created incandescent lamps which were long-lasting. After experimenting with many filament i.e., carbon and platinum, he concluded using the carbon filament in the lamp which lasted for around 13.5 hours.