Final answer:
The longbow's supremacy was ended by the advent of firearms and gunpowder that allowed greater range, speed, and effectiveness in combat.
Step-by-step explanation:
The ultimate demise of the longbow as the weapon supreme in England during the 15th century can be attributed to the advent of firearms and gunpowder (option C), which offered a range of tactical advantages over traditional archery. Firearms became increasingly accurate, could fire farther and faster, and they diminished the importance of heavily armored cavalry by enabling infantry to engage targets at a distance. Additionally, as firearms technology improved, they became more reliable and easier to use, further contributing to the shift away from longbows in military combat.