Choose the word which is different from the rest.

The answer is D. Pool.

A lake is a large body of water surrounded by land. A sea is a large body of salt water that is connected to an ocean. A river is a large natural stream of water that flows in a channel to the sea or another river. A pond is a small body of water that is usually surrounded by land.

A pool is a man-made body of water that is usually smaller than a lake or a pond. It is often used for swimming, bathing, or other recreational activities.

The key difference between a pool and the other options is that a pool is man-made, while the others are natural.