熟悉四级阅读理解题型的同学应该都了解，英语四级考试的阅读理解材料大多选自《时代》《卫报》《今日美国》等外刊。要想阅读理解这部分拿到高分，必须在平常多阅读，掌握新词汇，锻炼阅读速度。

为此小编每日精选了《卫报》《时代》等外刊上的文章供大家进行阅读练习。

本篇阅读材料“灰尘背后的那些事儿”选自《时代》(原文标题：What's in Household Dust? Don't Ask 2010.2 23)。如果大家觉得比较简单，就当作泛读材料了解了解，认识几个新单词或新表达方式也不错。如果大家觉得这些材料理解上有难度，不妨当做挑战自己的拔高训练，希望大家都有进步^^

It's hard to get too worked up about dust. Yes, it's a nuisance, but it's hardly one that causes us much anxiety — and our language itself suggests as much. We call those clumps of the stuff under the bed dust bunnies after all, not, say, dust vermin.

to get worked up 为某件事生气;不开心

clumps of 一团一团的

dust bunny 积尘;灰兔子(关于灰尘的比较萌的说法)

But there's a higher ick factor to dust than you might think. And there's a science to how it gets around — a science that David Layton and Paloma Beamer, professors of environmental policy at the University of Arizona, are exploring.

get around 传播;散播

Layton and Beamer, whose latest study has been accepted for fall publication in the journal Environmental Science & Technology, knew a lot about their subject even before they set to work. Historically, everyone from chemists to homemakers has tried to figure out just what dust is made of, and the Arizona researchers drew their preliminary data mostly from two studies of household dust conducted in the Netherlands and the U.S. The American survey in particular was a big one, covering six Midwestern states. Layton and Beamer also included a localized study in Sacramento, Calif., that focused particularly on lead contamination. What all those surveys showed was decidedly unappetizing.

figure out 理解;解决;计算

The specific dust mix in any household differs according to climate, age of the house and the number of people who live in it — not to mention the occupants' cooking, cleaning and smoking habits. But nearly everywhere, dust consists of some combination of shed bits of human skin, animal fur, decomposing insects, food debris, lint and organic fibers from clothes, bedding and other fabrics, tracked-in soil, soot, particulate matter from smoking and cooking, and, disturbingly, lead, arsenic and even DDT.

"There are more [components]," Beamer says. "Dust is a hodgepodge of all sorts of things. It would probably be impossible to make a list of all the possible items."

But dust's ingredient label is not the whole story, since all of those flecks and bits behave differently and present different levels of health risk. To investigate those factors more closely, Layton and Beamer developed a computer algorithm that looked at the size, source and toxicity of dust particles as well as how easily they enter the house, if they ever exit and, if so, by what route. That information, by extension, can provide at least a rough sense of the dust load in your own home.

As a general rule, the majority of household dust — about 60% — comes from outside, through windows, doors, vents and, significantly, on the soles of your shoes. Smaller dust particles — from 28 to 49 microns, or thousandths of a millimeter — tend to stay on your shoes. The rest is shaken off inside. A higher share of the dust that floats in the air gets deposited, but again, there's a lot that determines how much any one home will get.

"Here in Arizona," says Beamer, "where we leave our windows open most of the year and have an arid climate, we would probably have a higher ratio." Industrial centers or sootycities have plenty of dust too, though for different reasons.

arid adj. 干旱的;不毛的

ratio n. 比例

There's not much to fret about in simple particles of dirt or organic materials such aspollen (though they can trigger allergies), but lead, arsenic and DDT can be a more serious matter. About one-third of the arsenic in the atmosphere comes from natural sources — volcanoes principally. The rest comes from mining, smelting, burning fossil fuels and other industrial processes. Even in relatively low concentrations, arsenic is not without risk, especially to small children who play on the floor and routinely transfer things from their hands to their mouths. The same is true for lead, which comes less from wall paint — the source most people would expect — than from auto exhaust, smelting and soil deposits. "Lead loading on floors is a key determinant of blood-lead levels in children," Layton and Beamer wrote in their paper.

fret about 因……焦急;为……烦恼

particle n. 颗粒;微粒

pollen n. 花粉

low concentration 低浓度

determinant adj. 决定性的 n. 决定因素

The fact that DDT is still in house dust is a surprise to most people, since the pesticide was banned in the U.S. in 1972. But a house is a little like a living organism: once it absorbs a contaminant, it may never purge it completely. "Dust in our homes," says Beamer, "especially deep dust in our carpets and furniture, is a conglomerate of substances over the life of the home and can provide a historical record of chemicals that have entered it."

contaminant n. 污染物;致污物

purge v. 净化;清除

The mess that originates within the home is a lot easier to measure and control. The more people who live there, the more skin that's going to be shed, the more pets, the more animal fur. And, as Mom always warned, the more you walk around the house while eating, the more food debris you'll drop on the floor — which also attracts more insects that will die, decompose and add their own special zest to your dust. Cooking smoke and tobacco smoke, which are the most obvious contributors when they're being produced, actually make only a small contribution to what winds up on floors and surfaces. The tiny size of the particles makes them likelier to rise and adhere to other surfaces or simply remain in the air than to settle.

shed v. 散发;流出

wind up 卷起;扬起

It goes without saying that your home will never be dust-free, but there are ways to reduce your own dust loading — and it's important that you try. Dust mites, which feed on shed skin, produce allergens that are known triggers for people suffering fromasthma. Same goes for cockroach dust, especially in cities. No one needs much convincing about the wisdom of getting rid of arsenic, and the good news is that about 80% of it can be removed simply by cleaning floor dust regularly.

it goes without saying 不言而喻;不消说

allergen 过敏原;反应原

None of this means that dust poses a clear and present danger or that you need to take any extraordinary measures. Just clean regularly, don't smoke, eat at the table — and try not to freak out. Dust bunnies are still only bunnies; you may just want fewer of them.

freak out 吓坏了;崩溃

Question time:

1. How does dust come into our houses?

2. What's the key factor of blood-lead levels in children according to Layton and Beamer' papaer?

3. How to get rid of the dust in house?