48. In the mitochondrial electron transport chain, as Complex III and Complex IV participate in electron transfer, which of the following important ion transfer phenomena occurs simultaneously? (A) Protons (H+) are transferred from the mitochondrial matrix to the intermembrane space. (B) Protons (H+) are pumped from the intermembrane space into the mitochondrial matrix. (C) Calcium ions (Ca2+) are pumped from the intermembrane space into the mitochondrial matrix. (D) Potassium ions (K+) are pumped from the mitochondrial matrix to the cytoplasm.