Disadvantage: Pollution to the environment by waste oil.

• A. Sensitivity to dirt
• B. Temperature dependence (change in viscosity)
• C. Pollution to the environment by waste oil
• D. Unfavorable efficiency factor

Answer: (C)

Waste oil handling creates an environmental pollution risk because used oil can carry contaminants and additives that, if spilled or improperly disposed of, can taint soil, surface water, and even groundwater. This environmental impact is a fundamental drawback because it drives the need for careful collection, containment, and recycling or proper disposal, which adds cost and regulatory requirements. The other factors listed describe how oil behaves in operation—sensitivity to dirt, how viscosity changes with temperature, and an efficiency-related issue—which affect performance rather than posing an environmental hazard. So the environmental pollution aspect stands out as the key disadvantage.