Final answer:
The practice among the listed options that is also illegal in many jurisdictions is using a cellphone without a hands-free device while driving, as it is commonly prohibited to reduce road distractions and improve safety.
Step-by-step explanation:
All of the following practices are dangerous to do while driving. Which of these is also illegal? 1) Using a cellphone 2) Eating or drinking 3) Adjusting the radio or music player 4) All of the above. While all of these behaviors can be risky and result in distracted driving, the legality of these actions can vary by jurisdiction. However, the most commonly illegal action across various locations is using a cellphone without a hands-free device while driving. Many places have laws that specifically prohibit the use of hand-held mobile phones to promote road safety and reduce distractions. In contrast, eating, drinking, or adjusting the radio are not specifically illegal in most jurisdictions, although they could contribute to distracted driving and could lead to violations if they result in unsafe driving behavior. Using a cellphone, eating or drinking, and adjusting the radio or music player are not only dangerous practices while driving but are also illegal in many places. Laws regarding these activities may vary by jurisdiction, but in many places, there are regulations against distracted driving, which can include activities like using a cellphone or engaging in other behaviors that take attention away from driving. It's essential to be aware of and comply with local traffic laws to ensure safety on the road.