The correct answer is C. An incandescent light bulb produces a continuous visible spectrum.
Visible light spectrum is the term used to define the range of wavelength that can be discerned by the human eye. However, the vast share of electromagnetic waves are invisible to humans. Below is the graph comparing the visible light range with the entire electromagnetic spectrum.
An incandescent lamp is a light source powered by electricity. Its mechanism involves heating a tungsten filament, which produces light. Although Thomas Edison is widely famous for creating an incandescent lamp, the first person who patented the mechanism was Joseph Wilson Swan.
The continuous type of visible spectrum is produced by warm substances. For example, the sun emits continuous visible light spectrum. Because of the mechanism used to light the incandescent lamp, its spectrum of electromagnetic radiation is also considered continuous.