The correct answer is: C. Two banks of meandering river.
A meander belt is the area of land that is affected by a meandering river. It includes the river channel itself, as well as the floodplain and the adjacent uplands. The width of a meander belt is the transverse distance between the two banks of the river.
The apex point of a meander is the point where the river bends most sharply. The crossing is the point where the two banks of the river are closest together.
Apex point of one curve and apex point of the reserve curve are not relevant to the width of a meander belt.