The author mentions all of thefollowing attributes that enable a homing pigeon to return h

外贸易兴旺。汉朝开拓的丝绸之路通向了中西亚乃至罗马。各类艺术一派繁荣，涌现了很多文学历史哲学巨著公元100年中国第一部字典编撰完成，收入9000个字，提供释义并列举不同的写法。期间科技方面也取得很大进步。发明纸张水中日晷(sundials)，以及测量地震的仪器。汉朝经历了四百年，但统治者的腐败导致了它的灭亡。

的军事防御工程，东起辽东半岛(Liaodong Peninsula),西至临洮。这就是举世闻名的万里长城。长城是世界一大奇迹，由数百关隘(pass)、堡垒(fortress)、塔楼和城墙构成。每隔一定距离，就建一个烽火台，敌人接近时，发出警报。位于北京的八达岭长城、慕田峪长城和司马台长城都建于明朝时期。如今，长城每年都吸引着众多国内外游客前来参观。它不仅是艺术非凡的文物古迹，同时也是中华人民伟大力量与智慧的结晶。

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.

B) It needs to be understood that most paper and card is manufactured for a specific purpose， 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.

C) Paper can be made from an almost endless variety of cellulose-based material which will include many woods， cottons and grasses or which papyrus is an example and from where we get the word "paper". Many of these are very specialized， but the preponderance of paper making has been from soft wood and cotton or rags， with the bulk being wood-based.

Paper from Wood

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 cellulose fibers is produced. It is from this pulp that the final product is made， relying on the bonding together of the cellulose into layers. That， in a very small nutshell， is the essence 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 cellulose. Something called lignin. This is essential for the tree since it holds the cellulose fibres together， but if it is incorporated into the manufactured paper it presents archivists with a problem. Lignin eventually breaks down and releases acid products into the paper. This will weaken the bond between the cellulose fibers and the paper will become brittle and look rather brown and careworn. We have all seen 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.

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 increase 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 course， 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 whatsoever in carefully placing our valuable artifacts in paper or card that is going to hasten

their demise. Acid is particularly harmful to photographic materials， causing them to fade and is some cases simply vanish!

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 sell. 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 good quality acid-free paper will do little to guard the contents. The acid will get there in the end.

Paper from Rag

K) Paper is also commonly made from cotton and rag waste. This has the advantage of being lignin-free， but because 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 purchase from a reliable source though， since even rag paper and card can contain undesirable additives.

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 purchase 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.

1. The corn-flake packet is cheaper than high grade card.

2. There are a lot of materials which can be used for making paper， but the superiority ones are soft wood， cotton and rags.

3. During the whole manufacturing process， the final product is made from a pulp of cellulose fibres.

4. In order to make white paper and card， the makers will add bleach.

5. Liguin is essential for the tree but it will make paper easy to break.

6. Many paper producers will preserve lignin during manufacture， because leaving the lignin will make more paper from a tree.

7. Acid is particularly harmful to photographic materials.

8. If the lignin is removed from the paper， the paper will be more expensive.

9. Although free of lignin， paper made from cotton and rag waste can also cost more money than wood pulp paper because there is much less cotton and rag than trees.

10. What we can learn from "Paper from Rag" is that you had better buy archival materials from specialist suppliers.

善空气质量，努力提高人类生活水平。随着工业及交通运输业的不断发展，大量的有害物质被排放到空气中，使人们的健康受到威胁。因此，防治大气污染、控制污染排放就显得尤为重要。植物能过滤掉(filter out)各种大气污染物和净化空气，森林尤为显著，所以绿化造林(afforestation)是防治大气污染的比较经济有效的措施。

听力原文： Should Foreign Abbreviations Be Banned on TV?

Recently, CCTV banned the use of borrowed English abbreviations such as NBA, WTO and CPI in all its programs. Some people applaud the move, maintaining that it helps preserve the purity of the Chinese language. The media is deeply engaged in the ongoing Westernization of Chinese language. If the phenomenon is not stopped, Chinese will be gradually reduced from an independent expression system to a mixture of languages.

Others, however, shake their heads. It is not persuasive, they say, that the media shy away from foreign abbreviations to preserve the purity of the Chinese language and culture. After all, languages' integration is a very complicated process and it's irrational to impose a simple ban on certain words. Besides, the use of foreign abbreviations won't shake the status of Chinese as an embodiment of and the basis of the 5,000-year-old Chinese culture.

As far as I am concerned, there is no need to ban the use of foreign abbreviations on TV. A language is great, not because of its purity, but because of its tolerance to other languages. Chinese is so rich and beautiful because it constantly absorbs words, abbreviations and phrases from other languages. It's totally unnecessary to fear about the disappearance of Chinese if we allow English to mix with Chinese.

For this part, you are allowed 30 minutes to write a short essay on the topic of Should Foreign Abbreviations Be Banned on TV?. You should write at least 150 words according to the outline given below.

目前有些电视台禁止在节目中使用外来缩略语

1.对这种做法有人表示支持

2．有人并不赞成

3．我认为……

Should Foreign Abbreviations Be Banned on TV?

A.reading

B.return

C.happy

D.anywhere

E.kind