We all know that when there is a clear sky, the western sky appears red as the sun sets. From the information presented in the passage, this phenomenon would seem to be explained by which of the following?

  I.  Light meets more obstacles when passing parallel to the earth’s surface than when traveling perpendicular. Consequently, even red light is diffused.
  II.  The blue light may not make it through the denser pathway of the evening sky, leaving only the long light waves of red.
  III.  The short red light waves have more energy and are the only waves that can make it through the thick atmosphere of the evening sky.