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分类: 教育/科学 >> 外语学习
问题描述:
最好有论述草场退化与沙漠化的关系
解析:
Do you think of a desert as a hot, dry place where sand stretches as far as you can see? The Sahara in North Africa is like that, but most deserts are not. All deserts are dry, but some deserts are very cold. Plants and animals live in most deserts. People have learned to live in deserts all over the world.
Most deserts form because of air movements over the pla. Masses of dry air create deserts. For example, deserts can form where air currents go over mountains. Water gets squeezed out of the air as it passes over the mountains, and a desert forms on the other side of the mountains. Deserts can also form along some seacoasts where there are currents of cold water. There are o main bands of desert areas, one north of the equator and one south of the equator. The equator is an imaginary line that goes around Earth"s middle.
MAJOR DESERTS OF THE WORLD
The largest desert in the world is the Sahara. It covers a land area as big as the United States. Huge waves of sand called dunes cover most of the Sahara. The Sahara is very hot during the day, but it cools off at night because sand does not hold heat well.
The Gobi Desert in Asia is the largest cold desert. The Gobi covers parts of Mongolia and China. The Gobi gets very cold in the winter, but it can be hot during the summer.
A large desert covers parts of the southwestern United States and northern Mexico. There are also big desert areas in the Middle East, Australia, and South America.
DESERT PLANTS
Deserts get very little rain, but cactuses, trees, shrubs, and even wildflowers still manage to grow in some desert areas. These plants have special features, or adaptations, that help them get and store water. They have *** all leaves to keep water from escaping into the air. Some desert plants have long roots that reach water deep underground. Other plants, called succulents, can store water from a desert rainstorm in thick roots, stems, and leaves. Some desert plants grow for only a few days. They sprout after a rainfall. Then they die, and their seeds lie in the soil until the next rain es. The Sahara and deserts in the Middle East are so dry that they have few plants.
DESERT ANIMALS
Many kinds of animals also live in the desert. They include birds, insects, snakes, lizards, and some kinds of mammals. Desert animals have adaptations that help them survive. In hot deserts, centipedes, scorpions, and rattlesnakes burrow into the ground during the day to stay cool. Some foxes and rabbits that live in the desert have large ears that let body heat escape.
The camel is a large mammal with a hump on its back that lives in the Sahara and Middle East deserts. Camels can go for days without food or water. Camels use the fat in their hump for energy.
PEOPLE OF THE DESERTS
Millions of people live in deserts around the world. Some people mine copper or other metals in desert mines. Some people work on desert farms. Shepherds in the Middle East go from place to place looking for food and water for their animals.
People who live in deserts usually live near a source of water. They live on the banks of rivers that flow through deserts. They live on oases, places that have underground springs or wells. Water is so important to life in the desert that it must be used sparingly and be carefully protected.
People sometimes bring water to deserts. They dig c *** s to bring in water from rivers. They use the water for drinking and for growing crops. In the southwestern United States, people bring water from the Colorado River into the desert for people to drink and to grow crops.
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