In ancient Indian social structure, the term "aniravasita" is related to Sudras only. Let's understand the concept in detail.

**Ancient Indian Social Structure**
The ancient Indian social structure was based on the Varna system, which classified society into four main varnas or categories. These varnas were determined by a person's occupation and social status:

1. Brahmanas: The highest varna consisted of priests, scholars, and teachers who were responsible for spiritual and intellectual pursuits.
2. Kshatriyas: This varna comprised of warriors, rulers, and administrators who were responsible for protecting the society and maintaining law and order.
3. Vaishyas: The varna of merchants, traders, and farmers who were engaged in business and agricultural activities.
4. Sudras: The lowest varna consisted of laborers, servants, and workers who provided services to the other varnas.

**The Meaning of "Aniravasita"**
The term "aniravasita" refers to a person who does not belong to any of the four varnas mentioned above. It refers to people who were outside the Varna classification and did not have a specific social status or occupation assigned to them.

**Explanation of the Correct Answer**
The correct answer to the question is option 'C,' which states that the term "aniravasita" is related to Sudras only. This means that individuals belonging to the Sudra varna were considered "aniravasita" as they did not have a higher social status like the Brahmanas, Kshatriyas, or Vaishyas.

Sudras were considered to be at the bottom of the social hierarchy and were often engaged in menial and lower-status occupations. They were not entitled to the same privileges and opportunities as individuals from the higher varnas. Therefore, the term "aniravasita" is specifically related to Sudras as they were considered outside the Varna classification.

It is important to note that the Varna system was a rigid social structure, and individuals were typically born into their respective varnas based on their family background. Moving between varnas was extremely difficult, and individuals were expected to adhere to their assigned varna throughout their lives.

In conclusion, the term "aniravasita" in the ancient Indian social structure is related to Sudras only, as they were considered outside the Varna classification and did not have a specific social status or occupation assigned to them.