📖 Unit 7: Natural Wonders of the World - Reading lớp 9

If we were asked exactly what we were doing a year ago, we would probably have to say that we could not remember. But if we kept a book and wrote in it an account of what we did each day, we should be able to give an answer. In a way, this is similar to history.
Most people are proud to tell you what their ancestors did in the past. We may call this remembered history. But many things have been forgotten because we do not have any written account of them. Sometimes people kept a record of the most important happenings in their country, but often it was destroyed by fire or in a war. Sometimes there was never any written record because the people of that time and place did not know how to write. For example, we know a lot about the people who lived in China about 2,500 years ago because they could write and leave written records for those who lived after them. But we know little about the people who lived just 200 years ago in central Africa, because they had no writing system.
Sometimes, even if people cannot write, they may know something of the past. They have heard about it from older people, and often songs, dances, and stories have been made about the most important past events, and these have been sung about, acted and told for generations.

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The wheel

Before the wheel was invented thousands of years ago, the only way to get from one place to another was (26) __________ our legs or riding animals, such as horses, camels, or donkeys.

Wheels today are on all sorts of vehicles from cars to planes, from bikes to skateboards. We believe that the first wheels were invented to help move very heavy (27) __________. Humans discovered that something heavy was more easily moved by rolling something round. Eventually wheels were (28) __________ for carts and wagons.

The wheel is probably the most significant mechanical invention of all time. The first wheels are thought to have appeared in Egypt on chariots around 2000 BC. Just imagine the world today (29) __________ the wheel, not only in transportation but also in technology. Important applications of the wheel include the water wheel and the spinning wheel. More (30) __________ applications include the jet engine and the turbine.

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At 2,315 miles (3,726 kilometres), the Missouri River is nearly as long as the Mississippi River, into which it flows. Together the Missouri and the Mississippi form one of the world's longest river systems.

There are seven major dams and dozens of smaller dams on the Missouri. The dams use water from the river to produce electricity. They also create reservoirs, or artificial lakes, behind them. The reservoirs store water that is needed for cities and for irrigation of crops. Irrigation is important because most of the regions around the river have a fairly dry climate.

In addition to producing electricity, the dams on the Missouri are also used to control the water level of the river. Sometimes water is held back to prevent floods. At other times, water is released to keep the water level high enough for barges to float downstream.

By changing the natural flow of water in the Missouri, dams and reservoirs have altered the river's ecosystem. They have affected the depth and temperature of the water in different parts of the river. Such changes have made it difficult for some species, or types, of plants, animals, and fish to survive. A few wildlife species in the region are now endangered.

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Mount Everest (Mt. Everest) is the highest mountain (1) ________________ the world. It is 8,848 metres high. Mt. Everest was first climbed in 1953 by Edmund Hillary and Tenzing Norgay. Every year, a lot of people want to climb Mt. Everest.

It is very dangerous to climb Mt. Everest. The air is very (2) ________________ and cold. Most people carry bottles of oxygen; they could die without it. When the oxygen bottles are empty, people throw them on the ground. (3) ________________ strong winds rip their tents, people leave them behind. They do not have the energy to take the rubbish away. They only have enough energy to go down the mountain (4) ________________.

Rubbish is a terrible problem. Since people first began to climb Mt. Everest, they have left tons and tons of rubbish on the mountain. Several groups have climbed the mountain just to (5) ________________ the rubbish. When people plan to climb the mountain, they have to plan to take away their rubbish.