The correct answer is c) electron transport system.
Explanation: The electron transport system is the final stage of cellular respiration, and it occurs in the mitochondria of eukaryotic cells. This process is aerobic, meaning it requires oxygen to function effectively. During this process, electrons are transferred through a series of proteins embedded in the inner mitochondrial membrane, ultimately combining with oxygen and hydrogen ions to form water. This step is crucial for generating a large amount of ATP, the energy currency of the cell.
In contrast, glycolysis (a), lactic acid production (b), and fermentation (d) do not require oxygen and can occur under anaerobic conditions. Therefore, among the options provided, only the electron transport system is dependent on the availability of oxygen.