Answer:
Correct answer is The Ural Mountains.
Explanation:
The Caspian Sea is not correct answer as sea is marked with blue color.
The Sayan Mountains are more to the east, closer to the border with Mongolia.
The Caucasus mountains are between Caspian and Black Sea and that also is not correct.
Therefore, the only correct answer is Ural, as this mountains are also natural border between Europe and Asia.
