Oil functions as a source of lubrication, allowing moving parts to function as a single unit.
In a machine with many moving parts, oil typically serves as a source of lubrication, much the same way human joints require fluid. Its purpose is not to clean, fuel, or power machines, but is instead a supplement to the proper functioning of moving parts.
B Oil serves as a fuel for moving parts in a machine.
C Oil provides a source of power when paired with fire.
D Oil functions as a cleaning agent, allowing all moving parts to remain free of dirt and grime.