We are talking about the Neolithic period here, which was the time before stone tools began to be replaced by tools made of bronze and other metals.
我们这里在说的是新石器时代，是石器开始被青铜和其他金属制工具所取代之前的那个时代。
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Some of the world's finest stone architecture can be seen in the ruins of the ancient Inca city of Machu Picchu high in the eastern Andes Mountains of Peru.