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.

    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.

    We need animals. Every animal has its place in the balance(平衡) of nature. We should try to help save the animals.

    Some people think zoos are good places. The zoos give the animals the comfortable and safe living places. If the animals get hurt or ill, people will take care of them. The zoo is a good place to know the rules in the wild world. We can be much closer to nature. We can know more about the animals in the zoos by watching, listening even smelling instead of just looking at the pictures in books.

    Some people don't think animals feel happy in the zoos. Animals like pandas, wolves and bears usually live in the wild. They play and find food by themselves. They are free and happy in the wild. If they are in the zoos, food is enough and rooms are comfortable. They do not need to do their best to find food to eat or places to stay in. They just walk around, sleep day and night, but they are not free at all.

    I think we should build national parks as wild life nature reserves to protect animals. If we do nothing, animals will get fewer and fewer.

    Sharks(鲨鱼) are the most frightening animals in the sea. Sometimes we can see sharks swimming in the sea around Hong Kong. People put nets around some beaches to protect swimmers. When there is a "shark's flag", people must stay on the beach. It will be too late if a shark can swim sixty kilometres an hour to you.

    There are 30 kinds of sharks and 25 kinds of them are dangerous. The whale sharks are, very big. They can grow to 18 metres long, but they are not dangerous to people. The jaws(大白鲨) and the tiger sharks are the most dangerous kinds of sharks.

    Do you know all sharks must keep swimming, or they will go down?

All sharks can feel everything that happens around them. We must keep calm and don't make any noise when a shark is swimming near you.

    If a shark loses a tooth, a new one will grow out very quickly. So sharks always have many sharp teeth.