Which of the following behaviors is illegal while operating a vehicle?

Driving with an open container of alcohol is illegal while operating a vehicle due to the potential for impaired driving and increased risk of accidents. Open containers can indicate that a driver may have been drinking and can lead to violations of laws intended to keep roadways safe for everyone. This behavior specifically poses a danger, as it may encourage consuming alcohol while driving, or distract the driver from their primary responsibility of focusing on the road.

Listening to music, using a GPS device, and adjusting the air conditioning are generally permissible behaviors, provided they do not distract the driver significantly. It is important to stay attentive and aware of the surroundings while performing any such tasks, but these activities do not inherently violate traffic laws.