A Thirsty World
The world is not only hungry; it is also thirsty for water. This seems strange to you, since nearly 75% of the earth's surface is covered with water. But about 97% of this huge amount is from sea water, or salt water. Man can only drink and use the other 3% — the fresh water that comes from rivers, lakes, underground, and other sources. And we cannot even use all of that, because some of it is in the form. of iceberg (冰山) and glaciers (冰串). Even worse, some of it has been polluted.
At the moment, this small amount of fresh water is still enough for us. However, our need for water is increasing rapidly. Only if we take steps to deal with this problem now can we avoid a severe worldwide water shortage later on. A limited water supply would have a bad effect on
agriculture and industry.
In addition to stopping wasting our precious water, one useful step we should take is to develop ways of reusing it. Experiments have already been done in this field, but only on a small scale.
Today, in most large cities tanks, water is used only once and it eventually returns to the sea or runs into underground storage tanks. But it is possible to pipe water that has been used to a purifying (净化) plant. There it can be filtered (过滤) and treated with chemicals so that it can be used again just as it were fresh from a spring.
But even if every large city purified and reused its water, we still would not have enough. Where could we turn next? To the oceans! All we'd have to do to make use of the vast amount of sea-water is — remove the salt. This salt-removing process is already in use in many parts of the wodd.
The phrase "the word" in the first line of the passage refers to ______.
A.man
B.you
C.woman
D.they
第1题
A.膜内高水平的巯基
B.黏附素
C.大量的黏蛋白和糖蛋白
D.高密度的菌群
E.膜内多聚体基质形成的网络结构
第2题
A.膜内高水平的巯基
B.大量的黏蛋白和糖蛋白形成屏障膜
C.多聚体基质形成网络结构,同时对膜的稳定性和通过性起保持作用
D.高密度的菌群
E.黏附素
第3题
对牙菌斑的描述准确的是
A、牙菌斑结构中没有中间层
B、牙菌斑是一种生物膜
C、牙菌斑形成不需要经过获得膜形成阶段
D、非附着菌斑不属于牙菌斑
E、只有黏附到牙齿表面的才是牙菌斑
第4题
B、膜结构的完整性
C、高度密集的菌群
D、节制细菌的代谢
E、拮抗抗生素的作用
菌斑生物膜能够有效保护细菌,防止细菌被氧化损伤,其作用机制是通过A、膜内高水平的巯基
B、黏附素
C、大量的黏蛋白和糖蛋白
D、高密度的菌群
E、膜内多聚体基质形成的网络结构
菌斑生物膜内利于细菌食物摄取和贮存,控制基质成分的移动速度。其作用机制是通过A、膜内高水平的巯基
B、大量的黏蛋白和糖蛋白形成屏障膜
C、多聚体基质形成网络结构,同时对膜的稳定性和通过性起保持作用
D、高密度的菌群
E、黏附素
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