Two monochromatic light beams have wavelengths of 520 nm and 680 nm, respectively. Which statement correctly identifies their perceived colors?
(a) The 520 nm beam appears blue, and the 680 nm beam appears violet.
(b) Both beams appear green because their wavelengths are near the center of the visible spectrum.
(c) The 520 nm beam appears green, and the 680 nm beam appears red.
(d) The 520 nm beam appears yellow, and the 680 nm beam appears orange.