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 in the morning and sets at 6 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 night. North of the equator nights are longer than days. Winter is the season of long nights. Summer is the season of long days.

    Many wild animals, such as pandas, are in d{#blank#}1{#/blank#}. Often there is not e{#blank#}2{#/blank#} land or forests, so the animals do not have a safe place to live.

    There are only about 1,600 pandas in the wild today. Pandas do not have many babies, and baby pandas often d{#blank#}3{#/blank#}. The situation is getting more and more difficult. We need to p{#blank#}4{#/blank#} them.

    The government is s{#blank#}5{#/blank#} up nature parks and the pandas live in peace there.

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    Have you ever had dreams about building a robot? Or putting together a spaceship? Or even seeing your face made out of chocolate? Done. All you need is a 3-D printer.

    The possibilities of 3-D printing seem endless(无穷尽的）.All the user has to do is to design an object on the computer and choose a material to print in. The printers print in hundreds of different materials including glass, sugar and even skin! When the user presses(按）“print", the 3-D printer spreads the materials layer(层）by layer and like magic the object is produced.

    The first 3-D printer was invented in 1986 by an American, Charles Hull. But 3-D printing has only become cheap enough recently for most people to use. Designers now use 3-D printing to create unusual things. The Dutch artist Dirk Vander Kooj prints furniture made from old fridges. And doctors have used 3-D printing to print human body parts! The Telegraph reported in February that scientists from Cornell Medical College even printed a man-made ear.

    But like a lot of new technologies, if 3-D printing gets into the wrong hands, it can be dangerous.

    In 2011 a group of four men in the US used 3-D printing to produce ATM skimmers(提款机盗刷器).These were placed on an ATM and stole over $400,000 from users of the ATM. It is terrible to think that criminals like them might one day use a 3-D printer to print a gun.

    But for better or for worse, 3-D printing has been put into use. In a few years, you'll probably be wondering how you could ever live without your 3-D printer!

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    Football is so popular in China. Almost everyone is interested in this sport—the young and the old, boys and girls, and now even robots.

Recently at Hangzhou Guangming Middle School, kids from several schools played football with their robots.

    Robot football is very different from human football. Only two robots play in each match. The field is as big as a ping pong table. One half is black and the other is white. Each robot tries to catch the "football" and score a goal. The robot with more goals wins.

    Gao Linge, a boy from Hangzhou Guangming Middle School, helped make one of the robots for the match.

    "My school bought the main board (主板),"said Gao, 14. "Then I decided what my robot looked like and made a computer program for it."

    Gao's robot was eight centimeters tall and had two arms. It had four sensors (传感器) to "see" and "kick" the "football".

    Ying Xuehai, a 12-year-old student from Gao's school, also made a robot. His robot played against Gao's. The match decided who would go to the final game. Ying lost the game. So he gave many of his robot's parts to Gao.

    Even so, Gao's robot didn't win the final. It played well in the first five minutes. Then it slowed down. By the end of the match, it could hardly move. What was wrong? Gao and Ying found the problem—the robot ran out of batteries (电池)!

    "We'll solve the problem and beat the other schools next time!" said the two boys.

    Dinosaurs, one of the most successful groups of animals that have ever lived, evolved(进化) into many sizes and shapes. The word "dinosaur" was invented by Sir Richard Owen in 1842 to describe these "fearfully great reptiles(爬行动物) ".

    Some things to keep in mind about dinosaurs：

    ·Not everything big and dead is a dinosaur. Dinosaurs were a special group of reptiles. Although Pterosaurs(翼龙) were similar, they were not true dinosaurs.

    ·Not all dinosaurs lived at the same time. Different dinosaurs lived at different times. Although you can see Stegosaurus(剑龙) fought against Tyrannosaurus

(暴龙) in some movies like King Kong and Jurassic Park, no Stegosaurus ever saw a Tyrannosaurus. It's because Tyrannosaurus appeared on the Earth about 80 million years after Stegosaurus died out.