A surface is perceived as blue when it reflects shorter wavelengths and absorbs others. Shorter wavelengths correspond to higher frequencies in the visible spectrum. Blue perception is related to the absorption and reflection properties of surfaces.
In order for a surface to be seen as blue, the shorter wavelengths are reflected while other colors are absorbed and are therefore not perceived. The correct answer is (a) Shorter wavelengths.
It's important to understand more about light and color perception: Colors with a shorter wavelength and higher frequency bend most when refracted. In contrast to a blue filter, which absorbs all visible light other than blue light, a perfect blackbody would be modeled by absorptive surfaces because they absorb all incoming light and don't reflect any. When considering the frequency and wavelength of different colors, such as green and blue light, blue light has a higher frequency and a shorter wavelength than green light.