How does temperature affect the viscosity of fuel?

Viscosity is defined as the measure of a fluid's resistance to flow. In the context of fuel, temperature plays a significant role in determining viscosity levels. As temperature increases, the kinetic energy of the molecules within the fuel also increases, allowing them to move more freely. This results in a decrease in viscosity. Conversely, at lower temperatures, the molecular motion slows down, leading to increased cohesion among the fuel molecules and, therefore, higher viscosity.

This relationship between temperature and viscosity is crucial for fuel system maintenance, as fuels with higher viscosity can lead to issues such as poor flow characteristics, difficulty in fuel atomization, and challenges in pump operation. Understanding this principle helps ensure proper operation and maintenance of fuel systems, as fuel must remain within an optimal viscosity range to function effectively in engines and other machinery.

Given this information, C is the correct choice as it accurately describes the effect of temperature on viscosity: higher temperatures reduce viscosity while lower temperatures increase it.