The population of the Earth is growing faster. It is important that we look after the Earth. We need it!
The Earth gives us a lot of things. We also give the Earth a lot, but some of the things are not good.
In nature, when something dies, other animals and plants get food from it. Every animal or plant gives food for other animals or plants. However, animals can't get food from many of the things that we ‘give' the Earth. Animals and plants can't eat metal, plastic and glass. These things will stay in the ground for many, many years.

Some rubbish is very dangerous for plants and animals. In some places, many animals live together. One animal makes food for many more animals. If we put rubbish and chemicals in the water, the plankton(浮游生物) can die. If there isn't any plankton, many animals have nothing to eat.
So what can we do? Don't leave any rubbish in the countryside! Don't make so much rubbish!

Save the world's trees

    "When it comes tothe Earth, there is no time to waste." says the Earth Day Network. And that isright. Protecting our environment is very important, and World Earth Day wascreated in 1970 to ask more people to protect our environment. On April 22, peoplearound the world celebrate Earth Day.

Every year thereis a special topic, and this year it is "Trees for the Earth", so Earth Daythis year will be all about planting trees. They are planning to plant 7.8billion trees within the next five years.

That's a biggoal, and you might wonder why trees are so important. Because they can take incarbon dioxide (CO₂) and protect the air quality(质量). CO₂ isa chemical in our atmosphere, but humans make too much of it. Each person makesabout 2.3 tons a year, which is bad for the environment.

Well guess what!Planting new trees is important because people cut down a huge number of trees.Last year, there were 3 trillion trees in the world, about 139 billion inChina. But according to China Daily, the world's total number has been almostcut in half since human civilization(文明) began. That's because 15billion trees are cut down every year.

So we need toplant more to make up for（弥补）the ones we lost. One treecan take in 21. 8 kilograms of CO₂ per year. And it's still one ofthe cheapest and best ways to get rid of CO₂.

    But don't forget that we can also help the environment by cutting down on how much energy(能源) or water we useevery day. Every little thing helps.

根据短文内容，回答问题（1-4），英译汉（5）。

    In many high schools, there are strict rules about using mobile phones. If your phone rings in class, for example, the teacher will be very angry.

    Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now, there is a ringtone called "mosquitotone (蚊子铃声)". Using it, students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?

    Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older, we are unable to hear some sounds with high frequencies (频率). As a result, a child or teenager can hear the mosquitotone ringtone, but someone of 20 or older can't.

    But sometimes, people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class, the student's phone rang. The 22-year-old teacher looked at the student and became unhappy. "I heard that. You know the rule: no mobile phone in class."

    Not all the students are interested in mosquitotone. Jerry Jones, a high school student of 17, says, "Using mosquitotone too often is bad for our hearing. I may use it for pleasure, but not in class. It's unfair(不公平的) to the teachers!"

    What do parents think of mosquitotone? "I think it is perfect for places like movie theaters," says Connie Neeson, 44. "Think about it. You're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However, it also has a bad influence（影响） on their study if students use it in class."

    How do animals communicate (交流) with each other? They have special "languages". In fact, they are using signals (信号). Different signals have different meanings.

    For example, when a bee (蜜蜂) finds food somewhere, it flies home quickly. It can't speak, but it can tell others by dancing. Other bees will know where and how far the food is.

    Some animals show their feelings by making sounds. For example, when a dog is angry, it barks (吠). At this time, you'd better stay away from it. Birds can make several sounds to show different meanings. Sometimes we humans show feelings by making sounds instead of by speaking. For example, when we feel painful (疼痛的), we cry "Oh!" or“Ouch!".

    We humans have languages and words. We can communicate face to face by speaking. We can write down what happened in order to remember clearly. We can also send (寄) messages to people far away. But animals can't.