A downside is that redwood is a soft, low-density material, so thicker lumber must be used to ensure a wall is strong enough to do the job.
不利的一面是，红木是一种柔软，低密度的物料，因此厚木材必须使用，以确保墙强大到足以完成工作。
Although its visual effect is so pronounced, dust is only a minor constituent of the material, extremely low in density, that lies between the stars.
尽管它的视觉效果如此显著，但尘埃只是位于恒星之间的物质的一个次要组成部分，其密度极低。
Its low density has led scientists to speculate that it may consist of porous, icy material.
土卫十六密度较低，科学家因此推断它可能由多孔冰物质构成。
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