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。
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。
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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