题干

实验表明,K+不能通过磷脂双分子层的人工膜,但如果在人工膜中加入少量的缬氨霉素(含12个氨基酸的脂溶性抗生素)时,K+则可以通过膜从高浓度移向低浓度处,这种物质通过膜的方式是(    )

A:自由扩散

B:协助扩散

C:主动运输

D:胞吞作用

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B

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                                                                     The Diet Zone: A Dangerous Place

    Diet Coke, diet Pepsi, diet pills, no-fat diet, vegetable diet… We are surrounded by the word “diet” everywhere we look and listen. We have so easily been attracted by the promise and potential of diet products that we have stopped thinking about what diet products are doing to us. We are paying for products that harm us psychologically and physically.

    Diet products significantly weaken us psychologically. On one level, we are not allowing our brain to admit that our weight problems lie not in actually losing the weight, but in controlling the consumption of fatty, high-calorie, unhealthy foods. Diet products allow us to jump over the thinking stage and go straight for the scale(秤)instead. All we have to do is to swallow or recognize the word “diet” in food labels.

    On another level, diet products have greater psychological effects. Every time we have a zero-calorie drink, we are telling ourselves without our awareness that we don't have to work to get results. Diet products make people believe that gain comes without pain, and that life can be without resistance and struggle.

    The danger of diet products lies not only in the psychological effects they have on us, but also in the physical harm that they cause. Diet foods can indirectly harm our bodies because consuming them instead of healthy foods means we are preventing our bodies from having basic nutrients. Diet foods and diet pills contain zero calorie only because the diet industry has created chemicals to produce these wonder products. Diet products may not be nutritional, and the chemicals that go into diet products are potentially dangerous.

    Now that we are aware of the effects that diet products have on us, it is time to seriously think about buying them. Losing weight lies in the power of minds, not in the power of chemicals. Once we realize this, we will be much better able to resist diet products, and therefore prevent the psychological and physical harm that comes from using them.