英语CET6长篇阅读练习题
2017年英语CET6长篇阅读练习题
Character iS the first and last word in the success. 以下是店铺为大家搜索整理的2017年英语CET6长篇阅读练习题，希望能给大家带来帮助!
Paper--More than Meets the Eye
A) We are surrounded by so much paper and card that it is easy to forget just how complex it is. There are many varieties and grades of paper materials, and whilst it is fairly easy to spot the varieties, it is far more difficult to spot the grades.piano是什么意思
B) It needs to be understood that most paper and card is manufactured for a specific purpo, so that whilst the corn-flake packet may look smart, it is clearly not something destined for the archives. It is made to look good, but only needs a limited life span. It is also much cheaper to manufacture than high grade card.
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hornetC) Paper can be made from an almost endless variety of cellulo-bad material which will include many woods, cottons and grass or which papyrus is an example and from where we get the word "paper". Many of the are very specialized, but the preponderance of paper making has been from soft wood and cotton or rags, with the bulk being wood-bad.
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D) In order to make wood into paper it needs to be broken down into fine strands. Firstly by powerful machinery and then boiled with strong alkalies such as caustic soda, until a fine pulp of cellulo fibers is produced. It is from this pulp that the final product is made, relying on the bonding together of the cellulo into layers. That, in a very small nutshell, is the esnce of paper making from wood. However, the reality is rather more complicated. In order to give us our white paper and card, the makers will add bleach and other materials such as china clay and additional chemicals.
E) A further problem with wood is that it contains a material that is not cellulo. Somethin
g called lignin. This is esntial for the tree since it holds the cellulo fibres together, but if it is incorporated into the manufactured paper it prents archivists with a problem. Lignin eventually breaks down and releas acid products into the paper. This will weaken the bond between the cellulo fibers and the paper will become brittle and look rather brown and careworn. We have all en this in old newspapers and cheap paperback books. It has been estimated that most paper back books will have a life of not greater than fifty years. Not what we need for our archives.bft考试
F) Since the lignin can be removed from the paper pulp during manufacture, the obvious question is "why is it left in the paper?" The answer lies in the fact that lignin makes up a considerable part of the tree. By leaving the lignin in the pulp a papermaker can increa his paper yield from a tree to some 95%. Removing it means a yield of only 35%. It is clearly uneconomic to remove the lignin for many paper and card applications.
G) It also means, of cour, that lignin-free paper is going to be more expensive, but that is nevertheless what the archivist must look for in his supplies. There is no point whatsoe
ver in carefully placing our valuable artifacts in paper or card that is going to hasten their demi. Acid is particularly harmful to photographic materials, causing them to fade and is some cas simply vanish!
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H) So, how do we tell a piece of suitable paper or card from one that is unsuitable? You cannot do it by simply looking, and rather disappointingly, you cannot always rely on the label. "Acid-free" might be true inasmuch as a test on the paper may indicate that it is a neutral material at this time. But lignin can take years before it starts the inevitable process of breaking down, and in the right conditions it will speed up enormously.
I) Added to this, as I have indicated earlier, paper may also contain other materials added during manufacture such as bleach, china clay, chemical whiteners and size. This looks like a bleak picture, and it would be but for the fact that there are suppliers who will guarantee the material that they ll. If you want to be absolutely sure that you are storing in, or printing on, the correct material then this is probably the only way.
J) Incidentally, acids can migrate from material to material. Lining old shoe boxes with go
od quality acid-free paper will do little to guard the contents. The acid will get there in the end.superiority
Paper from Rag
K) Paper is also commonly made from cotton and rag waste. This has the advantage of being lignin-free, but becau there is much less cotton and rag than trees, it also tends to be much more expensive than wood pulp paper. You will still need to purcha from a reliable source though, since even rag paper and card can contain undesirable additives.
陪驾多少钱一个小时L) A reliable source for quality rag papers is a recognized art stockiest. Many water color artists insist on using only fine quality rag paper and board.
M) The main lesson to learn from this information is that you cannot rely on purchasing archival materials from the high street. The only safe solution is to purcha from specialist suppliers. It may cost rather more, but in the end you will know that your important and valuable data and images have the best home possible.
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