Junior school students in Harbin，Heilongjiang, had a "long weekend". They had four days off from Oct. 19-22. It was not for any festival, but was caused by serious smog.
    The smog was caused by high levels of PM 2.5 in the air.
    PM 2.5 is small particles（微粒） of pollution in the air with a diameter （直径） of 2.5 micrometers or less. Waste gas from cars and factories is the biggest cause of PM 2.5 pollution.  On Oct. 17, the World Health Organization named air pollution a cause of cancer.
    To better protect children, cities are taking action.
    On Oct. 21, Harbin Education Bureau decided to close primary and junior high schools for two days.
    Beijing started a program on Oct. 22 which has a warning system with four levels. The red warning is the highest warning level. It means that the next three days will see serious pollution.
    When a red warning is issued（发布）, schools will close.
    If there's pollution that's not as serious, the Beijing Commission of Education will ask schools to stop PE classes and outdoor activities.
How will students be informed?
    "First, the Commission of Education will inform schools online," Ye Yan, head of Beijing Shijingshanqu Experimental Primary School, told Beijing Times. "Then teachers will text students' parents."
    Will the days off affect the study plan?
    "Missing school days will be made up during the summer or winter vacations,"  said Wang Hao, a physical education teacher in Beijing Chaoyang district.
    For students in Harbin who had the long weekend, they would go to school on the next two Saturdays.

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 most parts of the world, many students help their schools make less pollution. They join environment clubs. In an environment club, people work together to make our environment clean.

    Here are some things students often do.

    No-garbage lunches. How many lunch bags do you throw away after lunch? Environment clubs ask students to bring their lunches in bags that can be used again. Every week they will choose the classes that make the least garbage and report them to the whole school.

    No-car day. On a no-car day, nobody comes to school in a car including the students and the teachers. Cars give pollution to us, so remember：

    Walk, jump, bike, or run!

    Use your legs! It's lots of fun!

    Turn off the water! Do you know that some toilets can waste twenty to forty cubic meters of water an hour? In a year, that would fill in a small river. In the environment clubs, students mend those broken toilets.

    We love our environment. Let's work together to make it better.

    Every school day, we use schoolbags to carry all of our things to school. They are a big part of our lives. But have you ever thought about the history of the schoolbag?

    In the Han Dynasty (汉朝), students in old-style private schools used bamboo boxes to carry books to school. People consider the bamboo boxes to be the earliest schoolbags. They were usually two or three layers (层) in the box. Kids put different things like books, brushes, ink stones (砚) and paper in the boxes.

    Hundreds of years later, people developed a new kind of schoolbag called the budai, or the "hip-pocket". The budai was lighter than the bamboo box. With the founding (成立) of the People's Republic of China, military rucksacks (军用帆布包) became popular. Many people carried them when they were in school. Ask your grandparents or parents about these bags. Maybe they can tell you about their experiences of carrying them when they were in school.

    A new style of schoolbags has appeared in recent years. Many of them have colorful and fashionable designs (时尚的设计) on them, such as pictures of cartoons or pop stars. And they are more comfortable to use. Some students pull wheeled bags filled with heavy textbooks and others carry backpacks.

    Schoolbags are still changing. Can you imagine what future schoolbags will be like?

    For us humans, one of the greatest experiences is to taste all kinds of delicious food. But for penguins, they cannot get a taste of this happiness. That's because penguins can't actually taste the delicious flavors (味道) of their favorite food-fish!

    Scientists from the University of Michigan examined the genome (基因组)of five species of penguins. They found that no one can taste umami (鲜味),the flavor of meat or fish, the BBC reported.

    Many animals have five basic tastes: sweet, sour, salty, bitter and umami. But according to genetic data, penguins are believed to have only sour and salty tastes.

    These findings are surprising and puzzling. And scientists don't have a good explanation for them. But they have a few ideas.

    First, one of the umami genes doesn't work in cold temperatures. "It's about zero degrees when they eat cold fish," Zhang Jianzhi, the lead scientist, told the Daily Mail, so even if the penguins had a functional (功能的)gene, it might not work when they needed it.

    Second, penguins' tongues (舌头) are very special which may have something to do with their lack of taste. Instead of being covered with taste buds which help to taste food, penguins' tongues are very spiky. This is better for them to hold slippery (滑的) fish than tasting them. One study even showed that some types of penguins don't even have taste buds.

    However, penguins seem to be managing just fine.

    "Their behavior of swallowing food whole, and their tongue structure and function, suggest that penguins need no taste perception," said Zhang.

    We live on Earth. It's our home. But how much do you know about it? Let me tell you something about our Earth.

    The Earth is like a huge ball. Like the other seven planets, the Earth is running around the sun. It's the third nearest one to the sun. It takes the Earth about 365 days to run around the sun. At the same time, the Earth is going around itself. If you are in space, you can see lots of white clouds over the surface of the Earth. Through the clouds, you can see the blue colour of the oceans, and the brown colour of the land. About 70% of the Earth is covered(覆盖)with water.

    Why do we have day and night? When the half of the Earth is facing the sun, it's daytime. As the Earth turns, and this half is away from the sun, night is coming. And it's daytime(白天) for the other half.