Which of the following activities is considered a distraction while driving?

Dialing a cell phone is considered a distraction while driving because it requires taking a driver's attention away from the road to focus on the phone. This action involves both visual and cognitive elements—drivers must look at the phone screen to find the number and think about the call they intend to make, leading to divided attention that can significantly increase the risk of accidents.

In contrast, while listening to music, using GPS, and adjusting mirrors may also divert attention to some extent, they typically do not require the same level of engagement and focus as dialing a phone number. Listening to music is often automatic and familiar and doesn't demand visual involvement. Using GPS, if already set up, mostly requires periodic glances at the device, which can be managed effectively with practice. Adjusting mirrors is typically a quick action that drivers can perform while still keeping their eyes on the road. Thus, dialing a cell phone stands out as the most intrusive distraction in this context.