Carbohydrate digestion begins in the____________ whereas protein digestion begins in the ___________.

A. Aerobic respiration; anaerobic fermentation: Aerobic respiration primarily occurs in the mitochondrion, and anaerobic fermentation occurs in the cytoplasm. Therefore, this is incorrect.

B. Glycolysis; the citric acid (Krebs) cycle: Glycolysis occurs in the cytoplasm, breaking down glucose into pyruvate. The citric acid (Krebs) cycle takes place in the mitochondrion, where it further processes pyruvate for energy production.

C. The citric acid (Krebs) cycle; mitochondrial electron-transport: Both the citric acid cycle and the mitochondrial electron transport chain occur in the mitochondrion.

D. Anaerobic fermentation; glycolysis: Glycolysis occurs in the cytoplasm and is the first step in both aerobic and anaerobic pathways, but anaerobic fermentation also occurs in the cytoplasm, so this option is not accurate in distinguishing between processes happening in different locations.

The liver is indeed the largest gland in the human body, weighing about 1.5 kilograms in an average adult. It performs numerous vital functions, including detoxification, protein synthesis, and the production of biochemicals necessary for digestion (e.g., bile).