The correct answer is option 3 - Deserts. Deserts are areas that receive very little rainfall and are characterized by arid, dry conditions. In these regions, the water does not accumulate or drain into external bodies of water like rivers or lakes. Instead, it evaporates or seeps into the ground, leading to internal drainage. Deserts often have unique ecosystems adapted to survive in these harsh conditions, such as cacti and camels.

It is important to note that the other options do not represent areas with internal drainage. Plateaus are elevated flat lands, plains are low-lying flat areas, and mountains are elevated landforms. While these areas may have their own water drainage systems, they are not typically associated with internal drainage.