Well, first off you gotta think about what “erosion and deposition” mean. Once you got that figured out, think about what and how a pebble is created. The smooth surface and almost perfectly round; it has been picked up by erosion and the debris from the flowing water and the rock laying down, has caused its form and shape. From just a small rock to a pebble or a smoothed out rock you can skip. That’s been effected by erosion and deposition. I hope this helps!!!