Steel, concrete(混凝土) and glass are the usual materials in any skyscraper. But more high buildings are now using wood.

    In the last four years, Australia, Norway, England and Canada have all built wooden skyscrapers. The latest one is in Sweden, a new, 19-storey wooden hotel called "Sida vid Sida" (Side by Side).

    Why are wooden skyscrapers being chosen ahead of concrete ones? Let's find out.

    Is it strong enough?

    Wood has been used in many Chinese buildings for thousands of years, but is it strong enough for skyscrapers?

    "There's a lot of new materials made out of wood that are able to build big buildings," material expert Dr Michael Ramage told CNN when he was interviewed.

Architects (建筑师)have done thousands of experiment to make sure it is. They place layers of wood across one another coated with special glue to create very strong material.

Wood also lasts a long time and doesn't break down if it is well looked after. The examples include the rooftops of Beijing's Forbidden City and some 700-year-old houses in England.

Ramage also said on the internet that bamboo could be cut in special ways to make it even stronger than normal wood.

    Won't it catch fire?

    Wooden buildings sound dangerous when it comes to fire. But experts say they may be safer than concrete ones if there is a fire.

    "Wood doesn't burn in the way the public imagines," Ramage said. Very small pieces of wood catch fire easily, but very big pieces of wood are quite hard to set on fire, he said.

    Noise pollution is doing much harm to our health now. Noise, in fact, is unwanted sound and is a kind of invisible (无形的) killer. More and more students enjoy listening to music very much. When they listen to MP3 players, they like to turn up the volume (音量). Some people love listening to loud music. Furthermore, while watching TV, they keep the volume up. But they haven't realized that the noise is weakening their hearing. In fact, the noise not only influences each member in the family, but also makes a difference to the comfort of neighbors.

Noise pollution is a source of increasing misery (痛苦) to people in our society. If people are often disturbed by it, they may feel uncomfortable or upset. What's worse, the noise can make people mad sometimes. If a worker works in a printing factory for too long, his/her hearing loss is much faster than a common person working in a quieter environment. So everybody must pay more attention to noise pollution. Generally speaking, the following four types of noise should be watched out for:

    ◆Noise in the street

    ◆Construction site (建筑工地) noise

    ◆Noise at work

    ◆Transportation noise

    I think the local department (部门) should take measures to control the noise levels, but it's everybody's duty to keep a quiet environment.

    Are you able to send a letter with pictures and sounds to someone somewhere in the world without a stamp(邮票) on it? Using a computer you can send e-mails quickly and easily. The post is much slower than e-mail. E-mail can send its message to the other side of the world in seconds.

    E-mail is easy to use and it saves time and money. The differences in time in different parts of the world do not matter when sending e-mail. It's twenty-four-hour service(服务) that you can send e-mail at any time of the day or night. No one has to be there to get e-mail. It does not matter if your friends are in beds when you send e-mail to them, or you are seeing a movie at the movie theater when they send e-mail back.

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    For many years, scientists have said that the earth is getting warmer. Now they have found something new—hot cities! In the southern US, they have found that cities become very hot in summer. For example, the city of Atlanta in Georgia has roof(屋顶) temperature of up to 50^oC while it is 27℃ in the streets! At night, the outside of buildings stays so hot that the heat of the city causes storms over the city!

    China also has the same kind of problems. Every year more farmland is used for factories or offices. More housing is needed, too. As people become richer, they buy more cars. New roads are needed and new car parks are built in the city centers. This all makes cities hotter.

    It isn't easy to change the situation. City planners say that we should plant more trees in the middle of cities. Every new street should have trees on both sides, they say. Trees make the temperature lower, so we should have more trees in our parks and squares. We should also paint our roofs white. If we do this, they do not become so hot. Every roof in a hot and sunny country should have solar(太阳的) roof panels. The electricity from these can be used to run the air conditioners (空调)in the buildings.

    People continue to cut down forests around the cities. This makes the problem worse. Cities are growing faster and faster. By the year 2025, four fifths(五分之四) of the population will be living in cities. If we go on like this, there will not be enough farmland to feed everyone in the world.

    No Car Day first started by 34 cities in France on September 22, 1998. People started it to protect the environment. By now, more than 1,000 cities around the world have a No Car Day.

    The first No Car Day in China was in Chengdu in 2001. Other cities, including Taipei, Shanghai and Wuhan, also support(支持) the day.

    In Beijing, more and more people are joining in the program. It asks drivers to leave their cars at home for one day each month and walk or ride a bike to work. It also calls on Beijingers not to use cars on June 5(World Environment Day). The slogan(口号) for the day is, "If we drive for one less day, we can have one more nice day."

    So far, more than 200,000 drivers Show their support. "We can't decide the weather, but we can choose not to drive," said Wu Zhonghua, a car dub manager. Beijing is trying to have 238 blue sky days this year. In the first quarter of 2017, Beijing only had 52 blue sky days. This was 11 days less than the number for the same period the year before.

    We must do more for No Car Day.

    A myth is something that is not correct, but many people believe. There are a lot of myths about the human brain.

    One of the biggest myths is that we only use 10 percent of our brains. The next part of the myth is that if we can learn to use the rest of our brains, then we'll be much smarter. People say this all the time, but it's absolutely not true! The truth is that although we don't know everything about the human brain, we know that each part of it has an important function (功能). Modern scientists think the "10 percent myth" ridiculous(荒谬的).

    The other most popular myth is about being "right brained" or "left brained". According to this myth, people who use the right side of their brains are more artistic and creative. People who use the left side of their brains are better at math and science. This is as popular as the 10 percent myth, and it's also wrong. In 2013, a study at an American university examined the right brain and left brain myth. According to the study, we use both sides of our brains equally (相等地).

    It's true that we use different parts of our brains for different things. We use our left side for language more, and our right side when we need to pay attention. But there is no evidence (证据) that creative people use the right side more, or that scientific people use the left side more.

    We've talked about myths, so let's look at a few interesting facts about the brain. First of all, the brain feels no pain. Second, about 75 percent of the brain is made of water. It's also the fattest organ in your body. Here's another interesting fact about the brain. Around the time you turn 18 years old, it stops growing.