ANSWER: c
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They show that there was an ocean over the plains long ago, and fossils are always used to elaborate on the history of life/how it developed.
Twilight zone because the twilight zone is the deepest part of the ocean
A presidential system that is a constitutional, federal republic
Population distribution and density patterns can be useful to understand because they help to explain how and why people migrate and develop in certain places around the world. These factors influence human migration and development and are therefore important to understand if you seek to understand how the world has developed over time and what are the forces that are driving this development.
