那些双脚没有灰尘和痛处吗？
椭圆星系中有多达万亿颗古老的恒星，但几乎没有灰尘和其他星际物质。
Elliptical galaxies contain many older stars, up to one trillion, but little dust and other interstellar matter.
因为在冬天的大多数时候都会紧闭门窗，所以保持暖气过滤网干净、清洁、没有灰尘和碎石是很重要的。
Since we’re inside with doors and windows closed for most of the winter it’s important to keep the furnace filters clean and clear of dust and other debris.
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