Answer : 4. "Caspian Sea"
Explanation :

The correct answer is Caspian Sea. Caspian Sea: The Caspian Sea is the largest inland water body in the world. It is located to the east of the Caucasus Mountains and to the west of the vast plain of Central Asia. 750 miles (1,200 km) long from north to south, although its average width is only 200 miles (320 km).