The by-products of oxidation, as a result of water contamination of hydraulic oil, are generally __________.

Correct Answer: Option C — gums, varnishes, and acids

Water contamination in hydraulic oil promotes oxidation, leading to the formation of sludge, gums, varnishes, and acidic compounds. These contaminants degrade oil lubricity, accelerate component wear, and can cause valve sticking. Maintaining oil purity is critical for system reliability and preventing premature failure of precision hydraulic components.