The correct answer is C. Their mastery of gunpowder was crucial to the Ottoman Turks for capturing the Byzantine cities in the 15th century.
This event is known as the Fall of Constantinople or the Conquest of Istanbul and it consists in the capture of the Byzantine Empire by an Ottoman army in 1453. The capture of the city marked the end of the Byzantine Empire and denoted a crucial point in military history, since the Ottomans prevailed mainly thanks to the use of gunpowder which powered terrible cannons.
For some historians, the Fall of Constantinople marks the end of the Medieval period.
