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美国背景知识（上）
The continent\'s first inhabitants walked into North America across what is now the Bering Strait from Asia. For the next 20,000 years these pioneering settlers were essentially left alone to develop distinct and dynamic cultures.
The continent\'s first inhabitants walked into North America across what is now the Bering Strait from Asia. For the next 20,000 years these pioneering settlers were essentially left alone to develop distinct and dynamic cultures.
