1. The problem asks to identify which arc in the figure represents a semicircle. 2. A semicircle is an arc that represents exactly half of a circle, which means it subtends an angle of $180^\circ$ at the center of the circle. 3. Given the points and arcs: - Arc BEA - Arc ABD - Arc DAE - Arc EBA 4. Since the figure has center $O$ and points $A$, $B$, $D$, and $E$ on the circumference, the semicircle must be the arc that subtends a $180^\circ$ angle at $O$. 5. By the problem description, the arcs are named by their endpoints and intermediate points. The arc ABD includes points $A$, $B$, and $D$. 6. The arc ABD corresponds to half the circle because points $A$ and $D$ are on opposite ends of the circle, and $B$ lies on the arc between them. 7. Therefore, arc ABD is the semicircle. **Final answer:** B. arc ABD