填空题
If you wipe a finger across a household surface that hasn"t been cleaned in the last few days, chances are you"ll
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with dust. Look around and you"ll find the stuff everywhere, from the particles
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in the sunlight to the fine
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of dirt coating TV screens, bookshelves, and car dashboards. Dust comes from everything and, like death and taxes, you can"t avoid it. When things—shoes, rocks, plants, socks, anything at all—begin to
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, they release tiny pieces of themselves into the air. These
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bits settle everywhere, and because matter is always coming apart, dust production is a never-ending business.
In a typical household, dust
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mainly of things such as dead insect parts, sheets of skin, food particles, and pieces of fabric. But not all dust is the product of natural
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; we create amazing quantities of dust everyday. For example, a single puff (吸) of a cigarette contains an estimated four billion large dust particles. Industry of all sorts, from the
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of a piece of wood to large-scale steel manufacturing, creates particular kinds of dust. In short, dust is all around, even in the air we breathe. Because its particles are so small, dust is highly
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. Westward winds regularly blow dust from the Sahara desert across the Atlantic and into the
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above American coastal towns, where it contributes to some thrilling sunsets.