I think it is B. 1950's, but that is just a guess so if I'm wrong then I'm sorry
Hope this helps. :)
D. A frame is a list of the individuals in the population being studied.
'Vassals were the lowest class in the newly established government system's hierarchy.
<h3>
What is hierarchy?</h3>
A hierarchy is an arrangement of items (objects, names, values, categories, and so on). Hierarchy is a key concept in many disciplines, including architecture, philosophy, design, mathematics, computer science, organizational theory, systems theory, systematic biology, and social sciences.
A hierarchy can connect entities directly or indirectly, and it can connect entities vertically or diagonally. In a hierarchical system, the only direct links are to one's immediate superior or to one of one's subordinates, though a largely hierarchical system can also incorporate alternative hierarchies. Hierarchical links can extend "vertically" upwards or downwards by following a path with multiple links in the same direction.
To know more about Hierarchy visit:
brainly.com/question/13050649
#SPJ4
