The correct option is A The plague, feudalism
Feudalism was a system of mutual give and take. The nobles or landowners had vassals or farmers who worked under them. The noblemen had to protect the weak vassals, and in return, the vassals had to provide services to the nobles. But the farmers got very less at the end of the day. By the time the plague ended, the feudal system had nearly collapsed. In fact, the plague helped eradicate feudalism.