The correct option is A Investiture
Feudalism was the system in which land was granted to the nobles by the king. This land was in turn rented out to vassals.
In this system, there were two traditions- Investiture and Homage. Investiture involved the king assuring the vassal justice and protection while handing over the land. The homage tradition involved the vassal promising their loyalty and service to the feudal lord.
The Black Death is considered to be the first pandemic that wiped out a lot of Europe. It also helped in breaking down feudalism.