Which causes a meander to form in a river?

A.the deposition of sediments at the place where a river flows into an ocean
B.the erosion of rock where a river flows over it and erodes the softer rock
C.the deposition of sediments on a wide, sloping area at the bottom of a mountain
D.the movement of the river through easily eroded rocks or sediments

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B. the erosion of rock where a river flows over it and erodes the softer rock