The word "They" in paragraph 2 refers to ______.

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The Amazon rainforest is home to more than a third of all the world's species of plants, birds and animals. Twenty per cent of all the birds in the world live in the rainforest. Scientists have discovered thousands of types of plants and animals that can only be found there. There are thousands - probably millions more that we haven't discovered yet. There are at least 2.5 million species of insects there. Imagine what would happen if they all lost their home? It couldn't happen, could it? Unfortunately, it's happening right now. Yet, the rainforest is big. But it's getting smaller. The problem is that people are cutting down the trees, mainly to make room for cows. These provide meat and make money for their owners. This process of cutting down trees is called ‘deforestation'.

The good news is that it is slowing down. In 2004, for example, more than 27,000 square kilometres were cut down. That's an area bigger than Wales. In 2006, because of all the campaigns to save rainforest, it dropped to just over 13,000 square kilometres. The bad news is that it's not enough. Scientists predict that by 2030, the rainforest will have become smaller by 40%. It's possible that by the end of the 21st century, the rainforest will have completely disappeared. With deforestation, thousands of the animals, birds, fish and plants that live in the Amazon rainforest lose their home, their natural habitat. Some of them move to other areas, but most of them die. Many species have already become extinct, and many more will if deforestation continues. That will change the balance of life in the rainforest and could cause enormous problems to the region's ecosystem.

There's another problem too. Trees and plants are a vital source of oxygen. If we cut them down, we lose that oxygen. But it's worse than just that. With deforestation, the trees and plants are burnt. This sends gases into the Earth's atmosphere, which stops some of the Earth's heat escaping. That then leads to the temperature here on the ground going up. This increase in the world's temperature is called 'global warming', and most scientists believe it's a very serious issue. If they stopped deforestation, it might help prevent global warming

Which title best summarises the main idea of the passage?

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The costs and benefits of global warming will vary greatly from area to area. For moderate climate change, the balance can be difficult to assess. But the larger the change in climate, the more negative the consequences will become. Global warming will probably make life harder, not easier, for most people. This is mainly because we have already built enormous infrastructure based on the climate we now have.

People in some temperate zones may benefit from milder winters, more abundant rainfall, and expanding crop production zones. But people in other areas will suffer from increased heat waves, coastal erosion, rising sea level, more erratic rainfall, and droughts.

The crops, natural vegetation, and domesticated and wild animals (including seafood) that sustain people in a given area may be unable to adapt to local or regional changes in climate. The ranges of diseases and insect pests that are limited by temperature may expand, if other environmental conditions are also favourable.

In its summary report on the impacts of climate change, the Intergovernmental Panel on Climate Change stated, "Taken as a whole, the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.”

What is the main idea of the passage?

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Centuries ago, man discovered that removing moisture from food helped to preserve it, and that the easiest way to do this was to expose the food to sun and wind. In this way the North American Indians produced pemmican (dried meat ground into powder and made into cakes), the Scandinavians made stockfish and the Arabs dried dates and apricots.

All foods contain water - cabbage and other leaf vegetables contain as much as 93% water, potatoes and other root vegetables 80%, lean meat 75% and fish anything from 80% to 60% depending on how fatty it is. If this water is removed, the activity of the bacteria which cause food to go bad is checked.

Fruit is sun-dried in Asia Minor, Greece, Spain and other Mediterranean countries, and also in California, South Africa and Australia. The methods used vary, but in general the fruit is spread out on trays in drying yards in the hot sun. In order to prevent darkening, pears, peaches and apricots are exposed to the fumes of burning sulphur before drying. Plums for making prunes, and certain varieties of grapes for making raisins and currants, are dipped in an alkaline solution in order to crack the skins of the fruit slightly and remove their wax coating, so increasing the rate of drying.

Nowadays most foods are dried mechanically; the conventional method of such dehydration is to put food in chambers through which hot air is blown at temperatures of about 110°C at entry to about 45°C at exit. This is the usual method for drying such things as vegetables, minced meat, and fish.

Liquids such as milk, coffee, tea, soups and eggs may be dried by pouring them over a heated horizontal steel cylinder or by spraying them into a chamber through which a current of hot air passes. In the first case, the dried material is scraped off the roller as a thin film which is then broken up into small, though still relatively coarse flakes. In the second process it falls to the bottom of the chamber as a fine powder. Where recognizable pieces of meat and vegetables are required, as in soup, the ingredients are dried separately and then mixed.

Dried foods take up less room and weigh less than the same food packed in cans or frozen, and they do not need to be stored in special conditions. For these reasons they are invaluable to climbers, explorers and soldiers in battle, who have little storage space. They are also popular with housewives because it takes so little time to cook them.

What is the main idea of the passage?

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Earth is richly supplied with different types of living organisms which co-exist in their environments, forming complex, interrelated communities. Living organisms depend on one another for nutrients, shelter, and other benefits. The extinction of one species can set off a chain reaction that affects many other species, particularly if the loss occurs near the bottom of the food chain. For example, the extinction of a particular insect or plant might seem inconsequential. However, there may be fish or small animals that depend on that resource for foodstuffs. The loss can threaten the survival of these creatures and larger predators that prey upon them. Extinction can have a ripple effect that spreads throughout nature.

In addition to its biological consequences, extinction poses a moral dilemma for humans, the only species capable of saving the others. The presence of humans on the planet has affected all other life forms, particularly plants and animals. Human lifestyles have proven to be incompatible with the survival of some other species. Purposeful efforts have been made to eliminate animals that prey on people, livestock, crops, or pose any threat to human livelihoods. Some wild animals have been decimated by human desire for meat, hides, fur, or other body parts with commercial value. Likewise, demand for land, water, and other natural resources has left many wild plants and animals with little to no suitable habitat. Humans have also affected nature by introducing non-native species to local areas and producing pollutants having a negative impact on the environment. The combination of these human-related effects and natural obstacles such as disease or low birthrates has proven to be too much for some species to overcome. They have no chance of survival without human help.

As a result, societies have difficult choices to make about the amount of effort and money they are willing to spend to save imperiled species. Will people accept limits on their property rights, recreational activities, and means of livelihood to save a plant or an animal? Should saving such popular species as whales and dolphins take priority over saving obscure, annoying, or fearful species? Is it the responsibility of humans to save every kind of life form from disappearing, or is extinction an inevitable part of nature, in which the strong survive and the weak perish? These are some difficult questions that people face as they ponder the fate of other species living on this planet.

What does the passage mainly discuss?