The correct answer is a) caste.
In India, the division of kin groups in Jatis is not based on a specific principle, varying from ethnic origins to geographical occupation, exhibiting some variance. While the Jatis have not presented a fixed hierarchy, they present notions of a rank achieved over time considering lifestyle and social, political or economic status and considering the fact that the caste has a direct impact in these factors, we understand why it is the more relevant idea.