专业英语课程考试试卷

专业英语课程考试试卷A卷

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READING MATERIAL A:

Plastic are remarkably useful materials, but one of their greatest advantages over other materials, their durability, is also one of their gr eatest handicaps. They don’t disintegrate. Once we dump them into the environment, they just stay there. Some plastic seem to last forever. One way to keep discarded plastics from overwhelming us is to recycle them, to use them over and over again. But there are different kinds of plastics, and one sort doesn't mix well with another. To reuse plastics we have to separate one kind from another so that we can combine all compatible plastics into one group and reprocess them as a whole. One way to sort them is by taking advantage of differences in the densities of different kinds of plastics.

If an era is known by the kinds of materials its people use to build the world they live in, then the Stone Age, the Bronze Age, and the Iron Age have given way to our own Plastic Age. Plastics form much of our packing and wrapping materials, many of our bottles and containers, textiles, plumbing and building materials, furniture and flooring, paints, glues and adhesives, electrical insulation, automobile parts and bodies, television, stereo and computer cabinets, medical equipment, video and audio tapes, records and compact disks, personal items including pens, razors, toothbrushes, and hairsprays, and even the plastic trash bags we use to discard our plastic trash, Except for our food, air, and water, almost every ordinary thing we come in contact with each day contains some kind of a plastic somewhere in, on, or around it. Or it comes to us wrapped in plastic. So many of our throwaway goods are made of plastic that, despite its lightness, the material currently makes up an estimated 7% of the total weight of all solid municipal wastes and is expected to grow to 10% by the year 2000. What's more, plastics are a highly visible part of what we discard, making up roughly a quarter of the entire volume of our trash.

Durable or fragile, rigid or flexible, sturdy or flimsy, dense or light, strong or weak, plastics provide us with inexpensive materials of virtually unlimited properties. With chemical ingenuity we can transform them into almost whatever shapes we wish with almost whatever properties we desire. And at their root, in the polymeric molecules that make up these extraordinary substances of our everyday world, lies not only one of the shining achievements of modern chemistry but, as we'll see at the end of this chapter, perhaps even the secret of life itself. We'll begin, though, by examining the difference between the plastics of our world and the polymers that form them.

Plastics and Polymers

Plastics, especially the plastics of our most common commercial products, are extraordinary kinds of materials that we can shape into virtually any form we want. The word itself comes from the Greek plastikos, ''suitable for molding or shaping.'' We can form them into round, hard, resilient bowling balls, draw them out into the thin, flexible threads of synthetic fibers, mold them into intricately designed, long-running machine parts, or flatten them into flimsy but tough sheets