Final answer:
The Crusaders overcame the Justinian walls using cannons and gunpowder, which breached the walls after a 57-day siege, leading to the fall of Constantinople in 1453.
Step-by-step explanation:
The Crusaders managed to overcome the Justinian walls not by the means listed in options A, C, or D, but rather through the use of superior weaponry, specifically the advent of cannons and gunpowder. On May 29, 1453, after a 57-day siege, the Ottoman guns breached the walls, and the soldiers rushed into the city of Constantinople.
The use of early firearms and cannons changed the nature of sieges, allowing the Ottomans to finally break the impregnable walls that had protected Constantinople for centuries.