The idea that the oldest rock will always be the bottom layer of a series of rock layers is called the principle of _.

answer: c

explanation: i have done that passage before

the historians cited in the article all agree with one another about the cause of the civil war. despite coming from different backgrounds and cultures, the historians agree that slavery was the root cause of the civil war. the fact that all these historiansgenerally agree with one another makes their shared viewpoints more reliable and valid, especially because the historians have different backgrounds and all work for the well-respected institutions of howard university, clemson university, and the university of colorado.

a is the final ! : )