Which of the following is required when changing lanes?

Using turn signals is crucial when changing lanes because it communicates your intentions to other drivers on the road. This action helps in maintaining safety, as it alerts them to your planned maneuver, allowing them to react accordingly. Signaling also helps prevent accidents by ensuring that other vehicles are aware of your movements, which is essential for safe driving practices.

While headlights are important for visibility, especially in low-light conditions, they are not specifically required for lane changes. Honking the horn can be used in emergencies to alert other drivers, but it is not a standard practice for signaling lane changes and could potentially startle other drivers. Checking the weather is important for driving safety in general, but it is not directly related to the act of changing lanes. Therefore, using turn signals is the correct and most relevant action required when changing lanes.