They identified four different lead-based substances, two of which were man-made, not natural.

他们鉴定出四种不同的含铅物质，其中两种是人工合成的，并非天然物质。

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They identified four different lead-based substances, two of which were man-made, not natural.

他们鉴定出四种不同的含铅物质，其中两种是人工合成的，并非天然物质。

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