Which causes a meander to form in a river?

Question

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

Answer 1

the movement of the river through easily eroded rocks or sediments