Explanation:

- Varna system:

- Represents the division of society into four main hereditary classes (Brahmins, Kshatriyas, Vaishyas, Shudras).

- Seen as a 'vertical' social structure in traditional Indian society.

- Correct Answer.

- Jajmani system:

- Defines a traditional system of economic and social relationships in Indian villages.

- Focuses on a reciprocal exchange of services, not a caste hierarchy.

- Sanskritization:

- Refers to the process by which lower caste groups attempt to adopt behaviors and habits of higher castes to improve social status.

- Related to mobility, not a unit of caste structure.

- Endogamy:

- Practice of marrying within a specific social group or caste.

- Concerned with marriage customs, not classification hierarchy.