What emergency equipment must be carried on a vehicle with a registered gross weight exceeding 3,700 kg?

Answer: C — Two flares or two reflectorized devices

Vehicles with a registered gross weight exceeding 3,700 kg must carry two flares or two reflectorized devices. A spare tire is not related to emergency equipment and it is recommended to carry it regardless of the vehicle's weight. A GPS device may be helpful in emergency situations, but it is not a required piece of equipment. While having a first aid kit is important, it is not specifically mentioned as a requirement for vehicles exceeding 3,700 kg. Therefore, the only correct option is C, two flares or two reflectorized devices.