Under what circumstance can you legally use a cell phone while driving?

Answer: C — To make a 911 emergency call

Using a cell phone while driving is heavily regulated to ensure road safety, and one of the key exceptions to the rules is making emergency calls. When it comes to legal usage of a cell phone while driving, making a 911 emergency call is explicitly allowed. This is because emergencies can arise that require immediate communication with emergency services, and the ability to call for help can save lives. In contrast, reading messages or making personal calls can distract drivers from the road, increasing the risk of accidents. While using GPS navigation is often permitted in some jurisdictions, it must generally be used in a hands-free manner or configured prior to starting the journey to minimize distractions. Thus, in the context of legality and public safety, making a 911 emergency call is the primary circumstance under which a driver can use their cell phone legally while driving.