Unit 21

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Our universe has many planets , and the planet we are living on is the earth , which is covered by oceans and continents

我们的宇宙中有许多行星，而我们居住的这颗行星是地球，它被海洋和大陆所覆盖。

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How much do you know about this planet ?

你对这颗星球了解多少？

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Do you want to know more about it ?

你想了解更多相关信息吗？

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Let's approach and explore the earth together

让我们一起走近并探索地球。

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Our earth has existed for hundreds of millions of years , and there are many marvellous sceneries formed during the period , such as dense rainforests on land , caves and stones in the mountains

我们的地球已存在数亿年之久，在此期间形成了诸多奇妙的景观，比如陆地上茂密的热带雨林、山峦中的洞穴与奇石。

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Streams and rivers flow through valleys , and waterfalls fall down from cliffs

溪流与江河穿行于山谷之间，瀑布从悬崖峭壁飞泻而下。

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At the border of oceans , there are coasts covered by sands , which can make us feel relaxed when lying on the shore

在海洋的交界处，有着被细沙覆盖的海岸，躺在岸边能让我们感到无比放松。

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Every day , we can see sunrise in the morning and sunset in the evening

每天清晨我们都能看到日出，傍晚则能欣赏日落。

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All of these allow us to enjoy the beauty of nature

这一切都让我们得以享受大自然的美。

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To live on this planet , food and water are important for humans

在地球上生存，食物和水对人类至关重要。

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Farming is the foundation because crops grown on the farmland can provide food for us and solve the problem of hunger

农业是根基，因为农田里种植的庄稼能为我们提供食物，解决饥饿问题。

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Water is necessary for both plants and animals

水对植物和动物都是必需的。

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Although the amount of sea water is large , freshwater resource is limited , and even worse , we are running out of it

尽管海水量巨大，淡水资源却十分有限，更糟糕的是，我们正在逐渐耗尽这些资源。

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Therefore , it is our duty to protect water resources on the earth and save water for next generations

因此，保护地球上的水资源并为子孙后代节约用水是我们的责任。

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Wildlife makes our natural world colourful , and there are giant animals like zebras and giraffes in Africa , kangaroos in Oceania , penguins in Antarctica and tiny creatures like mosquitoes in our world

野生动物让我们的自然界变得多姿多彩，非洲有斑马、长颈鹿等巨型动物，大洋洲有袋鼠，南极洲有企鹅，而我们的世界里也有蚊子这样的微小生物。

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However , more and more species are decreasing due to environmental destroy and human hunting

然而，由于环境破坏和人类捕猎，越来越多的物种正在减少。

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Many rare animals are killed , which has greatly damaged the ecological balance between humans and nature

许多珍稀动物遭到猎杀，这严重破坏了人与自然之间的生态平衡。

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Therefore , to protect our planet , we should get along well with other creatures on the earth

因此，为了保护我们的星球，我们应该与地球上的其他生物和谐共处。