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.

    What is the first thing you want to do when you see someone yawn(打哈欠)? You want to yawn, too! Yawning is contagious.

    Scientists have found that all people yawn. Babies start to yawn even before they are born. The earliest yawn takes place when a baby is still inside its mother. When young children are about one year old, they start to yawn when they see others yawning. That's why scientists seem to think yawning is contagious.

    It's no secret that yawning is contagious, but why do we yawn? Well, scientists are not really sure.

    Some think we yawn because we feel bored. Recently scientists studied two groups of students between the ages of 17 and 19. One group watched music videos, and the other watched a boring color test. Scientists compared the numbers of their yawns and found that the color test group yawned more times than the video group.

    Another reason about yawning has to do with breathing. Some scientists believe that when we are bored or tired, we breathe more slowly. As our breathing slows down, we cannot get rid of(去除) enough carbon dioxide (CO₂) in our bodies. When there is too much carbon dioxide, our bodies will tell the brains (大脑) to breathe deeply. The result is a big yawn.                                                           

    In 2007, scientists suggested a new reason. They said that the reason people yawned was to cool down their brains. These scientists found that people who were warmer than others yawned more often.

    Scientists are still trying to find out why yawning happens and why it is so contagious. But they are only sure that when one person yawns, almost everyone else nearby wants to yawn, too.

    Do you know why different animals or pests(害虫) have their special colors? Colors in them seem to be mainly used to 1 themselves.

    Some birds like eating locusts(蝗虫), but birds cannot 2 catch them. Why? It is because locusts change their 3 with the change of the colors of crops. When crops are green, locusts look 4 But as the harvest time comes, locusts change into the same brown colo 5 crops have. Some other pests whose colors are 6 plants are easily found and eaten by 7 So they have to hide themselves for lives and appear only 8 

    If you 9 animals' life, you'll find the main use of colors is to protect 10 Bears, lions and other animals 11 quietly through forests. They cannot be easily seen by hunters 12 their colors are much like the trees.

    Colors are useful not only on the land, but also in the 13 A kind of fish can 14 （液体) when they face danger. The liquid spreads over quickly, so they cannot be found by their enemies and can quickly swim away. That is 15 they can live safely though they are not strong at all. So colors are really useful to animals.

    The world's largest radio telescope was finished on Sept. 25, 2017 in China.

    FAST is a five-hundred-meter telescope. It is also called Tian-yan ("The Eye of Heaven"), with a dish the sire of 30 football grounds, deep in the mountains of southwest China's Guizhou Province. The giant dish is built on a howl-like valley.

    The surrounding area has "radio silence" as there are no towns and cities within a 5-kilometer radius (半径范围) and only one county center within 25 kilometers.

    FAST is made up of 4, 450 panels (面板). The second largest radio telescope is in Russia. The bigger dish will be able to pick up weaker signals (信号).

    The radio telescope is like an ear, listening to tell meaningful radio messages from white noise in the universe. With the help of the telescope, we can receive weaker and more radio messages far away in space. It will help us to search for intelligent life outside of the Galaxy (银河系) and explore the origins (起源) of the universe. "Any of its discoveries will lead to a Nobel Prize," said Joseph Taylor, a Noble Prize winner.

    The FAST project began in 2011. And the telescope is expected to remain the global leader for the next 10 to 20 years.

    The word 'day' has two meanings. When we talk about the number of days in a year. We are using 'day' to mean 24 hours. But when we talk about day and night. We are using 'day' to mean the time between sunrise and sunset. Since the earth looks like a ball. The sun can shine on only half of it at a time. Always one half of the earth is having day and the other half night. A place. is moved from day into night and from night into day over and over by the spinning(旋转)of the earth. At the equator(赤道)day and night are sometimes the same length, they are each twelve hours long. The sun rises at 6 o'clock in the morning and sets at 6 o'clock in the evening. For six months the North Pole is tilted(倾斜)toward the Sun. In those months the Northern Hemisphere(半球)gets more hours of sunlight than the Southern Hemisphere. Days are longer than nights. South of the equator nights are longer than days. For the other six months the North Pole is tilted away from the SUN. Then the Southern Hemisphere gets more sunlight. Days are longer than nights. North of the equator nights ate longer than days. Winter is the season of long nights. Summer is the season of long days.