Feudalism is the trade of service for what?

Feudal society is a military hierarchy in which a ruler or lord offers mounted fighters a fief (medieval beneficium), a unit of land to control in exchange for a military service. ... Individual lords would divide their lands into smaller and smaller sections to give to lesser rulers and knights.

Explanation:

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.