Answer:
D
Step-by-step explanation:
Since the question is asking for a positive the A cannot be the answer since it would be considered a negative. The caste system was created where each higher class member would provide something in exchange for something provided by that lower class. in example: knights offered homes and protection to peasants, in exchange for food. Although it may be true that some castes cannot move up the pyramid, there are exceptions and this would be considered a negative.