Flow : River :: Stagnant : ?

The answer is C. Pool.

A river is a large natural stream of water flowing in a channel to the sea, a lake, or another river. A stream is a small river or a natural watercourse smaller than a river. A pool is a small body of water, especially one formed by a natural depression in the ground or by the damming of a stream.

A canal is a man-made channel for water, especially one used for irrigation or transportation.

A pool is the most similar to a river in that it is a body of water that is

not flowing. However, a pool is typically much smaller than a river and is often located in a natural depression in the ground. A stream is also a body of water that is not flowing, but it is typically much smaller than a pool and is often located in a mountainous area. A canal is a man-made channel for water, and it is typically much larger than a pool or a stream.