2. 外语
  3. The library of congress in Washington, D.C., which【C1】______ the largest collection of books in the world, is fighting a battle

The library of congress in Washington, D.C., which【C1】______ the largest collection of books in the world, is fighting a battle

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问题      The library of congress in Washington, D.C., which【C1】______ the largest collection of books in the world, is fighting a battle against paper deterioration. The【C2】______ of the old books, often yellowed and torn,【C3】______ crumble when they are touched. The main culprit in the battle is the acidic paper that has【C4】______ making books since the nineteenth century.
     Air pollution and moisture【C5】______ the problem.【C6】______ , the books that are most【C7】______ destruction are not the oldest books. The paper in books produced【C8】______  the last century was made【C9】______ cotton and linen rags,【C10】______ are naturally low in acid. And the Gutenberg bible,【C11】______ five centuries ago, was made of thin calfskin, and is in【C12】______  good shape. But in the nineteenth century, with widespread literacy bringing a demand for a cheaper and more plentiful【C13】______ of paper, the industry began using  【C14】______  treated wood pulp for making paper.【C15】______ the chemical in these paper that is causing today’s problem. This problem of paper deterioration is one of【C16】______ concern. France, Canada, and Austria are all doing research into the new methods of deacidification. A new technology has been【C17】______ recently, in fact, that allows for mass deacidification of【C18】______ books at the same time. It costs less than microfilming and  【C19】______ preserves books in their original form.【C20】______ there will soon be treatment facilities all over the world to preserve and deacidify library book collections.
【C5】
选项 A、have added to
B、has added
C、added to
D、adding to
答案C
解析 add to增添，文章主要用现在时，而空气污染和潮湿问题加重，强调了对现在的影响。因此选用现在完成时，因此正确答案是C。
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