1. The problem asks to identify a relation that is reflexive, anti-symmetric, and transitive. 2. Definitions: - A relation is **reflexive** if every element is related to itself. - It is **anti-symmetric** if for any two elements $a$ and $b$, whenever $a$ is related to $b$ and $b$ is related to $a$, then $a = b$. - It is **transitive** if whenever $a$ is related to $b$ and $b$ is related to $c$, then $a$ is related to $c$. 3. A relation with these three properties is called a **partially ordered set (poset)**. 4. Therefore, the correct answer is **C) Poset**. Final answer: **C) Poset**.