b
(b) Both radio and light waves are \(EM\) waves, just in different frequency ranges. The wavelength of visible light is typically around the \(600\) nm range, which is \(6/1000\) of a millimeter (very small). Radio waves on the other hand, often wave wavelengths of a few yards long. For a wave to diffract around an object, the size of the object must be on the same order of the wavelength of the wave.