As the river enters the plain it gets twists and turns forming large bends known as_______.

Correct option is A

The answer is meanders.
Meanders are large bends in a river that are formed as the river enters the plain. They are caused by the interaction of water flowing through a curved channel with the underlying river bed. The force of the water erodes the river bank on the outside of the bend, while deposition occurs on the inside of the bend. This process gradually causes the meander to migrate downstream.
Other Option Detail:
· Stack: A stack is a geological landform typically found along coastlines. It is a vertical column or pillar of rock that stands isolated from the main cliff or shore. Stacks are formed through erosion, where the sea erodes the rock on a headland, and as the softer rock is worn away, the harder rock remains as a tall column.
· Ox-bow: An oxbow is a U-shaped body of water that forms when a meandering river takes a shortcut. As a river meanders, its bends become more pronounced over time. Sometimes, the meander bends become so tight that the river creates a new, shorter channel, cutting off the loop of the original river course. This cutoff loop becomes an oxbow lake, disconnected from the main river channel.
· Levees: Levees are raised embankments or natural ridges found along the banks of rivers. They are typically formed by the accumulation of sediment and debris during periodic flooding events. When a river overflows its banks during a flood, it deposits sediment on the floodplain. Over time, these deposits build up and create levees, which act as natural barriers to confine the river within its channel during future floods.