The piston skirt's primary function is to:

The primary function of the piston skirt is to guide the piston within the cylinder. The piston skirt is the portion of the piston that extends downwards, providing stability and alignment as the piston moves up and down within the cylinder. This guiding function is crucial for maintaining the proper clearance and reducing lateral movement, which can lead to excessive wear or even damage to both the piston and the cylinder walls.

While the other options relate to important functions in engine operation, they do not accurately describe the primary role of the piston skirt. Maintaining oil flow is related to other components in the engine, supporting the piston typically refers to the connecting rod's function, and sealing the combustion chamber is primarily the responsibility of the piston rings. Each of these plays a vital role in the engine's overall performance, but guiding the piston is distinctly the main function of the piston skirt.