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（长度）. 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（北极）is tilted（倾斜）toward the sun. In those months the Northern Hemisphere（半球）gets more hours of sunlight than the Southern Hemisphere（半球）. 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 are longer than days. Winter is the season of long nights. Summer is the season of long days.

B

    For many people of Norway(挪威), skiing(滑雪) is the best way to have fun in winter. Almost everyone can ski. Children learn to ski after they learn to walk. Long, long ago in Norway, there were no buses, trains or cars. People had to find a way to walk over the deep snow. Skis were the right answer!

    Although they love winter, the people of Norway are also happy to see summer come. They enjoy the out-door activities at any time of the year. In summer they swim and sunbathe near the beach. Some people go hiking and go mountain climbing. Sail-boating is also very popular during the warm sunny summer months.

    The Norwegians(挪威人), like people everywhere, find many in-door ways to have a good time. During the long winter they also enjoy movies. They like to read books from the libraries in all seasons. Family life is very important to the people of Norway.

    On April 2, we said goodbye to Tiangong I, China's first space lab. According to the China Manned Space Agency (中国载人航天), Tiangong I re-entered the Earth's atmosphere (大气层) and some of its debris (碎片) fell into the South Pacific Ocean.

    There are many spacecraft (宇宙飞船) that are still in orbit(轨道) above the Earth. After finishing their trips, they will all re-enter the Earth's atmosphere like Tiangong I.

    There are two types of re-entries: controlled re-entry and uncontrolled re-entry.

    Some satellites and manned spacecraft come back to the Earth in a controlled re-entry. Experts calculate (计算) the path of the falling spacecraft and its speed. Thy can guide the spacecraft to fall in a chosen area.

    Some spacecraft may have problems while in space after a certain amount of time. These spacecraft come back in an uncontrolled re-entry. It is hard to tell when and where these spacecraft will fall until the last few hours. The US space station Skylab came back partially uncontrolled in 1979. Parts of the station fell in western Australia, but no one was hurt.

    During re-entry, most of the spacecraft will burn up while passing through the Earth's atmosphere. Only a small amount of the debris will reach the ground. The debris typically ends up falling into the ocean, China Daily reported.

    Most of us know that Ikea is the world's biggest furniture company. However, did you know that it's also a pioneer in environmental protection?

    Ikea says it's working hard to improve the environment. The company has made huge efforts to cut the carbon emissions(碳排放)of its suppliers(供应商).Over the past five years, Ikea has helped its suppliers become 18 percent more energy-efficient. It managed to do so by bringing its suppliers together. The one that produces the least carbon emissions will be praised.

    Ikea has also invested(投资)heavily in clean energy. The company now operates more than 300 wind turbines(叶轮机)around the world. It has also set up nearly 750,000 solar panels(太阳能嵌板)on the roof of its stores. As a result, Ikea can produce 71 percent of the energy it uses, which are all from clean sources. In some countries，such a} Denmark and Finland，the company produces as much energy as it uses.

    Ikea has been buying forests as well. It owns nearly 750 square kilometers of forest.

    Last but not least, Ikea has tried changing customers' behavior(行为).It does so by improving product designs. In 2015, Ikea changed all of its lighting products into LED. This change alone, it says, has saved lots of electricity.