The ray OB is in common to the angles EOB and BOA.
To solve this problem, you need to determine what rays each angle has and what ray is in common to both angles.
Angle EOB has two rays. They are
ray OE
ray OB
Angle BOA also has two rays. They are
ray OB
ray OA
Looking at the available rays, the only ray in common to both angles is ray OB. So the answer is ray OB.
