Final answer:
The correct answer to which functions dams are used for is c. i and ii, as dams create reservoirs for drinking water and power turbines for electricity generation but are not beneficial for salmon migration.
Step-by-step explanation:
Dams are used to create reservoirs for drinking water and to power turbines that generate electricity. However, they can actually hinder salmon migration rather than create better conditions for it. Therefore, the correct options are only to create reservoirs for drinking water (i) and to power turbines that generate electricity (ii), making the answer c. i and ii.
Dams are critical in water resource management and energy production. They provide a consistent supply of drinking water and facilitate flood control. Dams also generate hydropower as a renewable energy source by converting the potential energy of the stored water into electricity. Conversely, they can negatively impact ecosystems and wildlife, particularly by obstructing the migration patterns of fish species like salmon. This has led to efforts to mitigate these impacts with structures like fish ladders. Yet, despite these, downstream passage remains a significant problem for juvenile salmon.