Once Thomas Edison learned that a filament inside a glass ball would conduct electricity and create a glow, his problem became finding the right material to use as a filament. One substance tried by Edison was platinum, which did indeed conduct enough electricity to create a glowing light, but unfortunately, it lasted for only a few hours. Edison tested thousands of materials, including plant material, from which he finally developed a carbonized cotton thread filament, which lasted for 15 hours. Edison continued experimenting with this idea until he finally produced a 16-watt bulb that lasted 1,500 hours. Today's light-bulb filaments are mostly made of tungsten, a metal that Edison wanted to try but that was unavailable to him at the time.
According to this passage, what made it possible for Edison to produce his first successful light bulb?
Modification of some plant material
Substitution of glass for platinum