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.

    Here is a page from a magazine called Future. Read the following information about things that may happen in twenty years.

    Cars will run on solar power (太阳能) and will be much cleaner and safer. For example, if you are too close to another car or if you are driving dangerously, your car will slow down or stop by itself.

    New cities will have to be built in the sea. Some cities on water will have two levels(层). People will live on the upper level, the lower level will be used for traffic, shops and factories.

    Biotechnology(生物技术) will make food better and healthier. Plants without insects or illnesses(病虫害) will be developed. The taste of fruit and vegetables will be better and food will be kept longer.

    Many new ways to cure(治愈) illnesses will be found. People will use products of genetic engineering (基因产品) to cure more illnesses. However, some new illnesses will appear.

    If your pen broke at school today, what would you do? You would go to a shop and buy a new one. What if you could simply print out a real, working pen with your 3-D printer without leaving your room?

    Ten years ago people could only see 3-D printing in science fiction movies. But now 3-D printing is here and it's bringing big changes.

    Unlike normal printing that can only copy a 2-D picture with ink. 3-D printing can build almost anything made from material. The printer layers(分层) the material in different shapes to create the object you want to be copied.

    The 3-D printer has been used to make many different things. People have made cups, cars and even an airplane with it. Doctors have been using 3-D printers for several years. People's nervous systems(系统) have been printed out in 3-D form in medical research. Some body parts have been printed and used in hospital. Several months ago, doctors used a 3-D printer to rebuild the face of a person who had a bad accident. In the future, it is expected that the printer will make human organs(器官)to save more lives.

    However there are drawbacks to the printer. At the moment, printing can be quite slow and it's still rather expensive. The average(平均的) price of a household printer is around $1,700, not including the cost of the materials.

    But as the technology develops, it shouldn't be long before disadvantages are improved. Only time will tell where this new technology will take us.

    Humans have learnt many things from nature. These things have helped us in our daily life. The latest thing is self-repairing clothing.

    Scientists have developed a special way for clothing to repair rips and tears by itself, without the need for sewing. It works with materials such as cotton, linen and wool. The scientists are from the Naval Research Office and Pennsylvania State University in the USA. Scientists Dr Walter Dressick and Dr Melik Demirel looked at how a squid can cling on to things so well. The research team found a protein in the rings of teeth that cover the suckers on a squid. The protein is similar to the one found in the silk that spiders use to make spider webs. It is very strong and elastic.

    The new protein has been developed as part of a coating, which is put on clothes. When the coating is dipped in water, the area around the rip or tear joins together in less than a minute. This could help clothes last longer and save money for us. It could also be useful for military and survival clothes. People like soldiers and mountaineers would be safer if they had clothes that could be repaired quickly and easily. Professor Demirel spoke about the invention. He said," The coatings are thin, less than a micron, so they wouldn't be noticed in everyday wear." Then he added, "Even thin, they increase the overall strength of the material. For the first time, we are making self-healing textiles."