Answer:
B. The Hundred Years' War
Explanation:
It is a matter of the process of elimination: the Crusades ended before the 14th century began, and the Avignon Papacy was simply a relocation of the popes of Rome. Furthermore, the French and English War did not take place till the 1700s. As such, the only probable answer is the Hundred Years' War.
To further prove this answer, due to the Hundred Years' War almost all of England territory in France was lost, and many French nobles died. Additionally, it led to a decline in trade, particularly Gascon wine and English wool, which was a volatile part of Britain's trade goods. And to add salt to the wound, both countries taxed their people at great rates to pay for the war, causing social unrest.
