The American attitude shifted in favor of rights for Native Americans. This is based on "Polls showed that Americans believed in rights for Native Americans". Why it's not B is because it wasn't the polling that contributed to the act, but what the polls showed which is C.
Most people in Southeast Asia raise livestock for a living
Well ancient Greece was an oligarchy (kind of like a democracy). Greece has City States, as well as Ancient Mesopotamia. Mesopotamia had kings though, but was ran like an Oligarchy.