Wind, water, ice, and gravity continually shape Earth's surface through the process of erosion. Different sizes of sediment tend to mix when being moved along by water.
Both statements are true. Wind, water, ice, and gravity are all forces that continually shape Earth's surface through the process of erosion. Erosion involves the wearing away and transportation of fragmented rock and soil. Different sizes of sediment do tend to mix when being moved along by water.
As water flows, it can pick up and carry various sizes of sediment, resulting in the mixing of different sizes of sediment.