Metalsmiths knew how to detect forgeries of precious metals by measuring their density, using Archimedes' method of submersion in water to measure volume.

当时的金属匠利用阿基米德把物体浸在水中测量体积的方法，知道如何检测假的贵金属物品。

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Unless rescued by a trained lifeguard, these drowning people can only struggle on the surface of the water from 20 to 60 seconds before submersion occurs.

除非是训练有素的救生员，这些溺水者只能在水面坚持二十到六十秒，之后会沉入水下。

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Unless rescued by a trained lifeguard, these drowning people can only struggle on the surface of the water from 20 to 60 seconds before submersion occurs.

除非是训练有素的救生员，这些溺水者只能在水面坚持二十到六十秒，之后会沉入水下。

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