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关于肺表面活性物质,下列哪项是正确的
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Read the following paragraph and point out its topic sentence, supporting sentences and concluding sentence.The forest is a sanitary agent. It is constantly eliminating impurities from the earth and the air. (1) Trees check, sweep, and filter from the air quantities of filthy, germ-laden dust.(2)Their leaves absorb poisonous gases from the air.(3)Roots give off acids, and these acids, together with the acids released by the fallen, decaying leaves, have a sterilizing effect upon the soil.(4)Trees help to keep the earth sweet and clean, and water which comes from a forested watershed is likely to be pure.(5)Many unsanitary areas have been redeemed and rendered healthy by trees planting.(6)
Anyway, even if one wanted to, one couldn’t put the clock back to an earlier age. (1)Knowledge and techniques can’t just be forgotten.(2)Even if all government money for research were cut off (and the present government is doing its best), the force of competition would still bring about advances in technology.(3)Moreover, one cannot stop inquiring minds from thinking about basic science, whether or not they are paid for it.(4)The only way to prevent further developments would be a global state that suppressed anything new, and human initiative and inventiveness are such that even this wouldn’t succeed.(5)All it would do is slow down the rate of change.(6)
把物料经过适当干燥处理，降低水分再粉碎的操作一定属于（）。
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