A titanic impact could have stripped away a portion of its rocky mantle, leaving behind a metallic core whose density is out of proportion with the original ratio of rock to metal.

超大碰撞可能剥去了水星的一部分岩石地幔，留下了一个金属核心，其密度与原来的岩石与金属的比例相比大得不成比例。

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Because their density is only just smaller than sea water, a portion around one tenth of the iceberg usually sits above the surface.

由于冰山的密度比海水要小，一般露出海面的部分只占冰山的十分之一左右。

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Fast food outlets should reduce the energy density of their menus as well as their portion sizes, the scientists said.

科学家们指出，快餐店不仅要降低食品的能量密度，而且要缩小食品的体积。

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