What is a nacelle commonly used for on an aircraft?

A nacelle is primarily used to house and cover an aircraft engine. This structure is designed to streamline the aerodynamics of the aircraft, reduce drag, and protect the engine from environmental factors while allowing for maintenance access. In many aircraft designs, the nacelle is an integral part of the overall design and serves both functional and aesthetic purposes.

The other functions mentioned in the other choices are not typically associated with nacelles. While stability, lift enhancement, and airfoil adjustment are critical components of aircraft aerodynamics and performance, these are not functions served by the nacelle itself. Instead, these roles are fulfilled by other parts of the aircraft's design, such as wings and control surfaces.