When are you allowed to use your mobile phone while driving?

Answer: A — When using a hands-free system

Using a mobile phone while driving is heavily regulated due to the risks it poses to safety. The correct choice is using a hands-free system. This allows you to make and receive calls without physically holding the phone, which helps keep your attention focused on driving. However, it's essential to ensure that operating a hands-free device does not divert your attention from the road. The other scenarios mentioned in the question are not permissible for the use of a mobile phone. Stopping at a traffic light does not qualify as being parked; your vehicle is still considered in motion in the eyes of the law. Using a phone while driving on the motorway is similarly prohibited, as the attention required for high-speed driving is critical. Lastly, being parked in a safe area is a more straightforward situation where you can lawfully use your mobile phone, as long as the vehicle is not in motion.