Final answer:
Flares, fuses, or reflectors are essential warning devices used to mark a disabled vehicle during both day and night to ensure road safety.
Step-by-step explanation:
Flares, fuses, or reflectors are warning devices used to indicate a disabled vehicle's presence to other motorists. They play a critical role in preventing accidents and ensuring safety on the road. While they can be used during both day and night, their primary purpose is to provide a clear warning in low visibility conditions, such as at night or in bad weather.
Specifically, when answering the question 'Flares, fuses, or reflectors are:', the correct option is 'd. B. and C. are correct'. These devices are not for heating a vehicle but are essential to alert other drivers to a stationary vehicle that may be a hazard, thereby increasing road safety.