<prompt> Which of the following statements best describes Background Radiation?Radiation in the background of nuclear reactorsRadiation in the background during radiological investigationsRadiation present constantly from natural sourcesRadiation from nuclear fall out  <response>: Background radiation refers to those coming from the environment of natural radioactivity at the eahs surface and the those from direct cosmic radiation that arrives at the eahs surface. Ref: Radiation Biophysics By Edward L. Alpen, Page 432; The Biological Basis of Nursing : Cancer By William T. Blows, Page 54, 56 