C. Opportunity cost
This is the opportuntiy that they lost. it costed them. Thus, opportunity cost for another opportunity.
Vladimir Lenin was famous he was a dictator in another country if that helps.
Many knights were professional warriors who served in the lord's army. ... In return, the lord provided the knight with lodging, food, armor, weapons, horses and money. Peasants, or serfs, farmed the land and provided the vassal or lord with wealth in the form of food and products.
