The correct answer is "alluvial fan." An alluvial fan is formed when sediment erodes away from an area due to a river's flow. To find the correct answer to this question, you can recall or research the process of sediment erosion by rivers. Rivers carry sediment, such as rock particles and soil, as they flow downstream. The force of the water can erode the surrounding land and transport the sediment. As the river reaches a flat or lower slope area, it slows down and deposits the sediment it was carrying, creating an alluvial fan. Remembering or researching this process will help you determine that the correct feature formed when sediment erodes away from the area as a result of a river's flow is an alluvial fan.