Hint: Ox-bow Lake is a stationary water body. This is formed as a result of constant friction that takes place when the surface of a certain type of land and state (or form) of water come in contact repeatedly.
The river flows down from a hill eroding the land as it flows to form a river valley. Although it is supposed to flow in a straight path, the obstructions caused by various objects or formation of land affects this linearity and causes the river to divert its path little by little over time, such that it forms a bend or loop-like structure.
The amount of water flowing in the outer side of the bend is more and speed is faster as compared to the lesser and slower inner part. This causes erosion of the land that is in contact with the outer side of the meander and deposition of the eroded material on the inside area. When this continuously happens for a longer period of time, the meander increases in size. As it becomes difficult for the river to follow through the loop it chooses a straighter path when the ends of the meandered bend are separated by sediments from the river and forms a horse-shoe-like shape that is called oxbow lake.
So, the correct answer is Option B.
Note: The ecosystem of the oxbow lake is the same as the river. But since it is a still water body it has a little different habitat.
For example, Kanwar Lake is the oxbow lake that is found in the state of Bihar. Being the largest freshwater oxbow lake it was popular for sightings of various kinds of migratory birds, but lack of care has made it a wetland with an almost dead ecosystem.