Question

Which statement is TRUE? Feudalism provided no benefits for noblemen during the medieval period. A vassal could buy out his lord. The system of cooperation known as feudalism ended around the 15th century. Vassals were exempt from feudal aid

Answer 1

The system of cooperation known as feudalism ended around the 15th century. 

Feudalism was a complex system of relationships between people of different classes.  The king stood at the top of the system, and nobles were viewed as holding their lands in exchange  for their military service to the king.  The nobles then had vassals underneath them.  And at the bottom of the system, depending on the upper classes for protection and laws, were the peasants, who gave a share of their produce to the lords above them as their part of the exchange.
As a dominant system of society in Western Europe, feudalism had faded by 1500.  One reason was that kings had begun to employ professional soldiers for their armies, rather than relying on the nobles to be called upon when needed.  Also, the plague of the Black Death that swept through Europe in the 14th century had disrupted the relationships between the nobility and the lower classes.  Aspects of feudalism persisted in Europe for a couple centuries, but the full system had reached the end of its dominance in society by the 15th century.  In France, all last vestiges of feudalism were abolished during the French Revolution of the 18th century.

Answer 2

"The system of cooperation known as feudalism ended around the 15th century" would be the only correct answer from the list, since an increase in wealth distribution made it a cumbersome system to deal with.