题干

生物大分子通常都有一定的分子结构规律,即是由一定的基本结构单位,按一定的排列顺序和连接方式形成的多聚体,下列表述正确的是(  )

A:若该图为一段肽链的结构模式图,则1表示肽键,2表示中心碳原子,3的种类有20种

B:若该图为一段单链DNA的结构模式图,则1表示磷酸基团,2表示脱氧核糖,3的种类有4种

C:若该图为一段RNA的结构模式图,则1表示核糖,2表示磷酸基团,3的种类有4种

D:若该图表示多糖的结构模式图,淀粉、纤维素和糖原是相同的

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C

同类题5

    Many cities around the world today are heavily polluted. Products (产品) arc not produced in a "green" way and people haven't realized the importance of buying and using environmentally-friendly products. These lead to the pollution problem. One result is that millions of tons of waste like glass, paper and plastics is produced (生产). The waste problem is difficult to deal with.
    However, today, more and more people are choosing “green” and expecting that the products they buy should be safe for the environment. Before they buy a product, they ask questions like these: “Will this soap be bad for the environment”"Can this metal container be reused or can it only be used once?”
    Over 20,000 people took part in a web survey (调查) on buying environmentally-friendly products. Among them, 8129 people say that they now consider the environmental safety of a product before they buy it. That is to say, companies must change the way they make and sell their products to make sure that the products are “green”.
    A few years ago, it was impossible to find green products in supermarkets, but now there are hundreds. Some supermarket products carry labels to show that they are green. Some companies have made the clean and safe products their main selling point in advertisements.
The growing need for a safer and cleaner environment is making companies rethink how they do business. The public will no longer accept the old idea of “buy it, use it, throw it away, and forget it”. As a result, the companies have to take action.