The correct answer is C) Odd number. According to the U.S. Aids to Navigation System, buoys that should be left to the port (left) side when entering from seaward are identified by an odd number. This is a key regulation that helps mariners navigate safely and maintain the proper side of the channel or waterway. The other answer choices are incorrect because: A) Group flashing characteristic does not necessarily indicate the side of the channel, B) Nun shape refers to the physical shape of the buoy, not the side it should be passed on, and D) White light does not specifically designate the side of the channel the buoy should be left on.