26. Cancer tissue microenvironments are often observed to be more acidic than normal tissues. Which of the following is the primary reason for this acidification? (A) Decreased blood flow to the tumor leading to reduced oxygen delivery and accumulation of carbon dioxide. (B) Increased activity of the electron transport chain in cancer cells, leading to increased production of protons. (C) Enhanced oxidative phosphorylation in cancer cell mitochondria, consuming bicarbonate buffers. (D) Increased rate of glycolysis in cancer cells, leading to increased production of lactic acid and protons. (E) Reduced activity of proton pumps on the cell membrane of cancer cells, inhibiting proton export.