39. What is the general order of available energy sources in muscles during strenuous exertion? (A) glycogen ＞ ATP ＞ glucose ＞ fatty acids ＞ phosphocreatine, (B) ATP ＞ phosphocreatine ＞ glycogen ＞glucose ＞ fatty acids, (C) phosphocreatine ＞ glucose ＞ ATP ＞ fatty acids ＞ glycogen, (D) ATP ＞ glycogen ＞ phosphocreatine ＞ fatty acids ＞ glucose, (E) phosphocreatine ＞ ATP fatty acids ＞ glucose ＞ glycogen.