2. 外语
  3. Plastics are materials which are softened by heat and set into last form 1.______ when are shaped in a mold. Some are natural; s

Plastics are materials which are softened by heat and set into last form 1.______ when are shaped in a mold. Some are natural; s

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问题     Plastics are materials which are softened by heat and set into last form 1.______
when are shaped in a mold. Some are natural; some are semi-synthetic, the 2.______
result of chemical action on natural substance; some are synthetic, built up
from the constituents of oil or coal. All is based on the chemistry of carbon, 3.______
with its capacity of forming chains. The molecules that compose them 4.______
(monomers) link together in the setting or curing process to form chains
(polymers), which give plastics their flexible strength. Some plastics retain
their ability to be softened and reshaped; as wax, they are thermoplastic. 5.______
Others set permanently in the shapes they are given by heat and pressure;
like bags, they are thermosetting.
    From industrial beginnings in nineteenth century, plastics have 6.______
struggled through a hundred and twenty years of glory, failure, disrepute
and suspicion on the slow road to public acceptance. Now, at last, one can
positively say that plastics are appreciated and enjoyed for what they are;
that they make modern life rich, more comfortable and convenient, and 7.______
also more fun. Plastics are warm materials, sympathetic with the human 8.______
touch, and their transformation into things that come into contact with human
beings is entirely appropriate.
    The fact there are plastic antiques comes as a shock to most people. 9.______
How can a material that seems so essentially twentieth century, and one
that is so much associated with cheap, disposed products, has a history 10.______
at all? It is a young technology, and a great part of the fun of collecting
plastics is that beautiful pieces of historical interest can still be found very
cheaply.
选项
答案is——are
解析 本题为主谓一致性错误。此句主语为all，谓语动词的单复数取决于all所指代的事物是单数还是复数，此处all指的是上文提到的三种材料，应为复数。
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