1. The correct answer is: 3. Formation of stalagmites and stalactites .
Groundwater can be defined as a flow of water under the ground. This water is usually slightly acid, because it is formed when rainwater absorbs CO2 as it falls. That carbonic acid water sinks into the ground and moves through pores.
Groundwater dissolves away solid rock, so it is natural erosion force. As it travels through cracks, it enlarges them and potentially forms cave.
Also, groundwater carries dissolved minerals in solution that might be deposited as stalagmites or stalactites.
2. As the river flows it makes contact with soil, breaks the rocks (weathering) and carries with it sediments: gravel, sand, silt and clay (erosion).
Then, when a river encounters water, it deposits such sediments onto a flat area and forms alluvium (deposition). These sediments form several layers - beds. The delta becomes a main channel that divides land masses into streams – distributaries that look like a maze.
