17. Contrary to popular belief, the light bulb, a mainstay of modern life, had been around years before Thomas Edison evercreated one. _____ Previous versions were unreliable, expensive, and didn’t last very long. Up to 20 other independentinventors were doing the same thing as Edison at the time, trying to build a better light bulb. Edison’s version of the lightbulb improved on the filament, used a sealed vacuum bulb, and had a lower voltage than others at the time. The result wasa marketable product that could last for hours.
(A) Edison’s contribution was nothing but to improve on it.
(B) Thomas Edison was credited with the formulation of the light bulb.
(C) Edison purchased patents for the light bulbs other people had developed.
(D) Edison’s design has been improved upon over the years.