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 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 are longer than days. Winter is the season of long nights. Summer is the season of long days.

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Find Which Direction Is South

    Do you have a good sense of direction? If not, please take with you a compass. But if you forget to take a compass, you can still find your way. 

    It's never a wise idea to believe that the family member who was good at the job of map-reading knows where the family is. You can tell by the troubled look on their faces that nothing on the ground seems to match the map. Never mind. The sun is shining and it's still morning. If you don't know the exact time, you can still find out where south is, but you'll need to be patient. 

    ①Find a straight stick and put it in the ground in a place where you can mark its shadow(a dark shape on a surface that is made when something stands between a light and the surface). 

    ②Try to position the stick as vertically(垂直)as you can. You can check this by making a simple plumb line(铅锤线). You haven't got one? OK, use a thread(线) from your clothes with a button(纽扣) tied at the end to act as a weight.

    ③Mark the end of the shadow cast(投射) by the stick.

    ④Wait about half an hour and mark the end of the shadow again.

    ⑤Keep doing this until you have made several marks. 

    ⑥The mark nearest the stick will represent the shortest shadow, which is cast at midday, when the sun is highest in the sky and pointing to the exact south. 

    ⑦Pick a point in the distance along the line between the shortest shadow and the stick.

    ⑧That point is south of where you are. 

    ⑨Now you can turn the map, like you did before, and find which way you should be travelling. 

    Bananas are the perfect snack. Not only are they sweet and delicious, but they are easy to carry around, so you can take them anywhere. Best of all, bananas provide different things that the human body needs!

    Bananas grow best in warm places that get lots of rain. They grow on plants that look like trees.

    The banana plant, however, is considered a herb rather than a tree because it doesn't have a strong, woody stem(茎，干). The plants can grow as high as 30 feet. When they reach their full height, flowers grow out from the stem. These flowers produce bananas.

    Two or three times each year, the plants produce fruit. The bananas grow together, which seem like "hands". A hand is made up of 10 to 20 bananas. Growers sometimes call bananas "fingers".

    Each bunch(丛) of bananas has about 15 hands, and so a whole bunch may have as many as 200 bananas and can weigh more than 100 pounds.

    After about three months, the bananas are ready to be picked. At this point, they still aren't the sunny yellow color of bananas. Farmers pick them when they're green. That's how they're shipped to stores. They turn yellow along the way and are ready to be sold.

    If you love bananas, you've got a lot of company. Americans have been enjoying bananas since the first shipment arrived in the United States in 1876. Today, American eat more bananas than any other fruit. More bananas are sold than apples and grapes together. Every American eats over 26 pounds of bananas each year!

    How do you deal with plastic bags from the supermarket? Throw them away or recycle them? How about eating them?

    The bags are not harmful to the environment, Humans and animals can safely eat them. Indian company EnviGreen has made a bag with natural materials. It looks and feels just like plastic, but can break down(分解) easily.

    Ashwath Hedge who set up the EnviGreen Company spent four years doing experiments(实验) with 12 natural materials. They include potato, corn, vegetable oil and banana. He made the materials into liquid(液体) and used the liquid to make the bag.

    Although the EnviGreen bag is more expensive than a common plastic bag, it has many advantages. According to the Wall Street Journal, it takes 1,000 years for common plastic bags to break down. But an EnviGreen bag can naturally break down in less than 180 days. It also breaks down in less than a day in water, and in less than a minute in boiling water. Hedge was happy to show it in his interview, he put an EnviGreen bag in water and ate it with a smile.

    There are more than 15,000 tons of plastic waste in India every day. But only 9, 000 tons are processed. In China, 3 billion plastic bags are used every day. Maybe the EnviGreen bag could be a solution(解决方法) to the world problem of plastic pollution.

    Man has a big brain(脑). He can think, learn and speak. Scientists always say that men are different from animals because they can think and learn. They know now that dogs, rats, birds can learn too. They are beginning to understand that men are different from animals because they can speak. Animals cannot speak. They make noises when they are afraid, or angry or unhappy. Apes(类人猿) can understand some things more quickly than humans. One or two of them can learn a few words. But they cannot join words to make sentences. They cannot think like us because they have no language(语言). They can never think about the future. Language is a wonderful thing. Man can build a modern world because he has language. Every child can speak his own language very well when he is four or five, but no animals learn to speak. How do children learn it? Scientists do not really know. What happens inside our body when we speak? They do not know. They only know that man can speak because he has a brain.