Answer:
D. ∠ROS
Explanation:
You want to know which angle is adjacent to angle SOT in the given figure.
Adjacent angles
Angles are adjacent when they share a vertex and a side, but no interior space (do not overlap). Usually, we are concerned with the smallest adjacent angle in any given direction.
Any angle whose name starts with TO_ will share vertex O and side OT with the designated angle SOT. The smallest such angle is ∠TOU.
SImilarly, any angle whose name starts with SO_ will share vertex O and side OS with angle SOT. The smallest such angle is ∠SOR. Of course, we can also name this same angle ∠ROS, which is what you see in the answer choices.
∠ROS is adjacent to ∠SOT.
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Additional comment
In some cases, you might say that angles TOQ and TOR are also adjacent to angle SOT. Likewise, angles SOQ and SOU might be considered to be adjacent to angle SOT. These angles meet the definition of adjacent angles, but it would be pretty unusual for them to be considered adjacent angles in a geometry problem.