Answer:
A. Dams are used to control flooding, and flooding deposits sediments needed for healthy soil.
Step-by-step explanation:
When a dam stops the course of a river, the fragments of earth and rock carried by the water (the flood) accumulate at the bottom of the river and the reservoir, instead of on the banks of the river. When the water from the reservoir is released, it comes without a flood, and since it is part of the material that enriches the farmland downstream, it deteriorates. In addition, the water leaving the dam carries the flood and continues to erode the land as it digs deeper into the river bed.