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Initially, humans used naturally occurring objects as tools (for instance, a sharp stone or a forked stick). Later, peo began purpos to sh wood a stone in tools. Bec of t perishable nat of wo, modern know of how it was used in prehistoric times is largely a matter of inference. With tools of stone, however, archaeologists are on firmer ground; there are a vast number of surviving artifacts. Throughout the world, flint was a favored material because of its unusual physical properties.
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参考答案：ple efully ape nd to ause he ure od ledge