43. Otto Warburg observed that, in conditions of normal oxygen tension, normal cells produced most of their energy via mitochondrial respiration. In contrast, over 50% of cancer cell energy was generated in the cytosol via glycolysis, with the remainder from the mitochondrial respiratory chain. This is termed the Warburg effect. The Warburg effect may be beneficial to cancer cells because it provides precursors for many biosynthetic pathways. These precursors include the followings, except : (A) amino acid precursors. (B) NADPH. (C) ribose sugars for DNA and RNA synthesis. (D) fatty acids for lipid synthesis.