《新世纪研究生公共英语教材阅读A》课文
Unit 3 Ocean of Sand
From The Guardian
1. There is more derts than sun and sand。 On the two pages you can find out how plants， animals and people manage to survive in the apparently barren places。
2. 生理期会怀孕吗All derts are dry。 The hot， sandy places we think of when we talk about derts are subtropical derts。 They are found near the Tropics of Cancer and Capricorn where the warm air which ris at the Equator sinks down again, giving a climate of clear skies and very low rainfall. The Sahara is almost one-third the size of Africa, and is nearly as big as the U. S. A. , the fourth largest country. It was not always a dert. 光明和黑暗Over millions of years it has been convered in ice, a， forests and grasslands.
3. Dert winds are usually dry. Some derts are in “rain shadow” areas where the winds have lost what moisture they had crossing high ground。 Others are in the middle of contin
ents where the winds blowing over them have lost any moisture gained from distant oceans. The Gobi dert in Mongolia in Asia is an example of such an inland dert. The Atacama in northern Chile is the driest dert on Earth。 Parts of the dert had no rain for 400 years丁香五月情, from 1570 to 1971, and in other parts， rains had never been recordedn. One of the sandiest derts is the Takla Makan。 Sandstorms can whip up the sand as high as 3, 048 m(10. 000 ft）。 Windblown sand in the Sahara can be so fierce that it will sandblast the point off a car or aeroplane. The temperature at night in a hot dert can drop below freezing, to -4℃(24℉). During the day, the sand can be as hot as 79℃（175℉）。
Living in a dert climate
4. Derts are difficult places in which to live. During the day they are very hot。 In the Libyan Dert in North Africa the temperature on 13 September 1922 reached 58C in the shade! But dert nights are often cold becau clear skies allow heat to escape into the atmosphere。 The lack of water caud by low rainfall is bad enough, but rainfall is also
highly unpredictable。 Years of drought can end in tremendous rainstorms。 Many dert areas are bare rock， or are covered with pebbles and gravel. Sand accounts for only about 15 per cent of the earth's dert regions. In some derts, the total rain for the year might fall in only two or three storms. But that is enough for plant eds to sprout and bloom, turning parts of the dert into carpets of flowers for a few days。
How plants survive
5. Within a few hours of rain falling, thousands of flowering plants will start to appear。 Seeds of plants such as the dert dandelion lie in the ground for years waiting for the rain。
6. The plants die as the dert dries out again， leaving their eds for the next rains。 Other plants have adapted to the harsh environment by storing water in their leaves， stems or roots。 The American saguaro cactus can hold 6 to 8 tones of water. Dert plants often have spreading root systems which extract every drop of moisture from the ground. The roots of the mesquite bush can be 20m deep.
7。 Plants generally lo water through pores in their leaves. To prevent this, dert plants have small waxy leaves and fewer pores幼儿园请假条怎么写。 Many clo their pores during the day so they do not lo moisture. To protect themlves against grazing animals， some plants have thorns or an unpleasant taste。 Cacti are protected by their sharp spines. Cacti are found only in American derts. The tallest are saguaros which can reach 15m (50 ft) tall， 雅思和托福哪个好考weigh 7 tons and live for 200 years. Water is stored in the stem and ud in times of drought如何洗螃蟹.
Animal life
8. Although derts em empty, few are without animals. Most animals shelter from the daytime heat in holes or burrows. The burrows trap moisture are stay cooler than the ground above。 In the cooler evening or at dawn红色英雄， the animals emerge.
9. Smaller mammals often have large ears. During the day, the animal los heat through its ears。 In the dark， large warn the animal of unen dangers.
10. Reptiles venturing out in daytime try to avoid touching the hot sand。 The Australian bearded lizard sometimes runs on its hind legs only. The aptly named sidewinder snake only touches the ground in two places。
11. All dert animals survive on little water. Many small animals live on the moisture in their food. Larger animals such as the camel can go without water for days， but drink huge amounts when they get the chance. A camel can drink 10 litres of water in a minute.
Dert peoples
12. Over thought of years, people have learnt how to survive in Derts. The San people of the Kalahari dert in southern Africa and the Australian Aborigines hunt animals and gather food plants。 They learn traditional skills from older people.
13. On the edges of the dert， nomadic peoples graze flocks of sheep and goats。 They are constantly moving to fresher pastures. Nomads such as the Tuareg of the Sahara in North Africa wear loo chothing to protect them sand and heat。 Tuareg men protect their faces with a veil.
14。 In some derts， oas (fertile areas) form around wells or springs。 Around oas there are ttlements and something farms. The mud-brick hous are kept cool by their thick windowless walls。
On the move
15. Derts are spreading。 Already 12 percent of the world‘s land is dert, and every year another 12 million hectares become uless for farming. As the following shows，dertification has many caus. The end result is that the soil becomes expod and is easily eroded。
