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  3. Get ready for a new kind of machine at your local gym: one that doesn’t involve huffing and puffing as you burn off calories. In

Get ready for a new kind of machine at your local gym: one that doesn’t involve huffing and puffing as you burn off calories. In

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问题     Get ready for a new kind of machine at your local gym: one that doesn’t involve huffing and puffing as you burn off calories. Instead, all you have to do is stand still for 30 seconds while the machine measures your body fat. It could then tell you exactly where you could do with losing a few pounds and even advise you on exercises for your problem areas. If the body fat scanner turns out to be accurate enough, its makers hope it could one day help doctors spot disease.
    The scanner works by simultaneously building up an accurate 3D image of the body, while measuring the body’s effect on an electromagnetic field. Combining the two measurements allows the researchers to work out the distribution of fat and water within. Neither method is new on its own, says Henri Tapp, at the Institute of Food Research in Norwich in the UK. "The smart thing is that we’ve put them in one machine."
    And it’s not just for gym users. The body fat scanner could be used to study fat deposition as children develop, while patients recover from injury, or during pregnancy. And since it uses radio waves rather than X-rays, Tapp’s device is safe to use repeatedly.
    Body shape is known to be a risk indicator for heart disease and diabetes. So accurately quantifying fat distribution could help doctors suggest preventive measures to patients before problems arise. At the moment, doctors estimate fat content from knowing body volume and water content. To a good approximation, says Tapp, anything that isn’t fat is water. The amount of water in the body is often measured by giving the subject a drink of water that contains a radioactive tracer. The level of tracer in the patient’s urine after three hours reveals the total water volume.
    To find out a body’s volume, subjects are weighed while totally submerged in water, and this is subtracted from their normal weight to give the weight of water displaced, and hence the subject’s volume. But it is scarcely practical for seriously ill people.
    There are other ways to directly measure body fat, such as passing a minuscule current between the wrists and feet. The overall fat content can then be estimated from the body’s resistance. But this method doesn’t take body shape into account—so a subject with particularly skinny legs might register a higher fat content than the true value. That’s because skinny legs — with a lower cross-sectional area — will present higher resistance to current. So the machine thinks the water content of the body is lower—rating the subject as fatter. Also, the system can only give an overall measurement of fat.
    Tapp’s method uses similar calculations, but is more sophisticated because it tells you where you are piling on the pounds.
For scanning, all the subject has to do is______.
选项 A、take up a form of workout in the gym
B、turn round the body fat scanner
C、lie on the electromagnetic field
D、stand in the system
答案D
解析 细节题。参见第一段第一、二句。不需要跑得气喘吁吁，只要在机器上站30秒，就会测量出身体脂肪。故选D。
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