The correct answer is option 'A': endogamy.

Explanation:
Endogamy refers to the practice of marrying within a specific unit, such as a kin group, caste, or a group of people living in the same locality. It is a social custom that restricts marriage options to individuals within a particular social or cultural group, while excluding potential partners from outside that group.

Endogamy has been prevalent in many societies throughout history and across various cultures. It serves several purposes, including maintaining social cohesion, preserving cultural traditions, and safeguarding the interests and privileges of a particular group.

**Importance of Endogamy:**

- **Preservation of cultural identity:** Endogamy helps to preserve the cultural identity of a group by ensuring that individuals marry within their own community. This allows for the transmission of cultural practices, values, and traditions from one generation to the next.

- **Social cohesion:** Endogamy can promote social cohesion within a community or group. By limiting marriage options to individuals within the same social unit, it promotes social solidarity, cooperation, and a sense of belonging among group members.

- **Maintenance of group boundaries:** Endogamy helps to maintain the boundaries of a social or cultural group. It reinforces the distinction between insiders and outsiders, strengthening the sense of unity and loyalty within the group.

- **Preservation of privileges and interests:** Endogamy can be a means to protect the interests and privileges of a particular group. By marrying within the same social unit, individuals can ensure the continuation of their social status, economic advantages, or political power.

- **Avoidance of conflicts or tensions:** Endogamy can help to prevent conflicts or tensions that may arise from intermarriage between different social or cultural groups. By restricting marriage options to individuals within the same group, it minimizes the potential for cultural clashes or disagreements.

In conclusion, endogamy is the practice of marrying within a specific unit, such as a kin group, caste, or a group of people living in the same locality. It serves various purposes, including the preservation of cultural identity, social cohesion, maintenance of group boundaries, preservation of privileges and interests, and avoidance of conflicts or tensions.