Why do plants grow in some places and not in others? Why does some land have so much growing on it, while other land has almost no plants growing on it at all?

    To grow,  plants need several things. One is warmth. In very cold places almost nothing grows. Plants also need water. In very dry parts of the Earth only a few unusual plants can grow. That's why dry deserts(沙漠) everywhere are almost not covered by trees or grass.

    Plants must also have a place in which to put down their roots and grow. They find it difficult to grow on hard land. The town is built on hard land. The plants here have only the soil(土壤) found between the cracks of the stones to grow in.

    Another thing plants must have before they can grow is food.

    What will happen if we try to make things grow on the sandy beach? A few plants, such as beach grass, will grow in sand, but most plants won't. Even if the weather is warm enough and we water the plants each day, many of them will die because the sand on this beach has almost no plant food.

    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

    According to the World Health Organization (WHO), environmental pollution kills 1.7 million children under the age of five every year worldwide. The WHO warns that child deaths will increase greatly if pollution continues to worsen. Of all the environmental problems, air pollution is being called the most dangerous.

    Most of these deaths take place in developing countries. However, WHO environment and health chief Maria Neira tells that air pollution is a leveler between rich and poor. Everybody, she says, needs to breathe.

    “You can be a very rich child, your parents very rich, but living in a place, in a city, which is very polluted. Then there is very little you can do because we all need to breathe. Air pollution is everywhere.”

    Maria Neira says one of the most important ways to reduce air pollution is to produce cleaner fuels for cooking and heating.

    “Almost half of the world population is using dirty fuels for cooking, heating, and lighting at home. And, this is affecting very much mothers who are staying and cooking at home, but the children who are around mothers—they are exposed as well.”

    Cleaning up how the world cooks, heats and lights homes and other buildings is a big-picture goal.

    But what can every one of us do to limit our family to air pollution?

    The U.S. Environmental Protection Agency has the following suggestions:

    ● Avoid walking where there is a high volume of vehicle traffic.

    ● Equip homes with air filters and air conditioning units.

    ● Limit your time outside if you live in an area that issues warnings about air quality.

    ● Wear high-grade, rated face masks tightly to the face when air quality is poor.

    ● If you live or commute in a very polluted area, remove your clothes and wash immediately after entering your house.

    However, the WHO stresses that governments around the world need to take the lead on ensuring that children grow up in a clean environment.

    When the weather is hot, you go to a lake or an ocean. When you are near a lake or an ocean, you feel cool. Why? The sun makes the earth hot, but it can not make the water hot. Though the air over the earth becomes hot, the air over the water stays cool. The hot air over the earth goes up, then the cool air over the water moves in and takes the place of the hot air. When you are near a lake or an ocean, you feel the cool air when it moves in. You feel the wind and the wind makes you cool.

Of course, scientists cannot answer all of our questions. If we ask "Why is the ocean full of salt?" scientists will say that the salt comes from rocks. When a rock gets very hot or very cool, it cracks (崩裂) , and rain falls into the cracks. The rain then carries the salt into the earth and the rivers. The rivers carry the salt into the ocean. But then we ask "What happens to the salt in the ocean? The ocean does not get saltier every year." scientists are not sure about the answer to the question.

    We know a lot about our world. But there are still many answers that we do not have, and we are curious(好奇的).

    Is your TV connected to the Internet? What about your chair, or your fridge? Probably they are not. But in the future, most things in your home may be connected, thanks to the so-called "Internet of things".

    The Internet of things may be coming sooner than you think. Earlier this year, Samsung CEO spent a lot of time talking about the Internet things. He said that three years from now, every Samsung product will be part of the Internet of things, no matter whether it's a remote control or a washing machine.

    So, how do household objects that are part of the Internet of things work? Well, think of a common chair. When connected to the Internet, the chair warms up when it knows the user has just walked into the room and is feeling cold.

    An Internet-connected camera could help people feel safer in their homes. It can know people's faces and has an infrared sensor（红外传感器）, so even if it's dark it can see when someone passes by and send you a message on your smart-phone to let you know who's there. If the person is someone you don't know, it can tell you that, too.

    But according to MIT Technology Review, whether companies are connecting dog food bowls or safety systems to the Internet, there may be some problems. For example, many early connected-home objects don't have much built-in security, which means they could be hacked（攻击）. Moreover, it could be difficult to get these new machines to work together especially when they are made by different companies. To fight this, many companies have joined the Open Interconnect Consortium, which had 45 members by late 2015.

    So, picture this: you enter your home. The temperature changes to make you feel comfortable. Your favorite music starts playing for you. Do you think that this would be a good thing? It may happen sooner than you think.

    Which animal do you think is "the king of the animals", the elephant, the lion or the tiger? They are all large and strong. But I think the tiger is "the king of the animals". If you watch carefully, you can find some black lines on the tiger's forehead(前额). The lines look like the Chinese word "WANG". The word means "the king of the world" in Chinese.

    Most of the tigers come from China and India. Tigers are dangerous animals. They look scary(吓人的). They like eating meat. They have yellow fur with black lines. They usually weigh about 200 to 300kg. Tigers can run fast. They run at a speed of 20 meters per second.

    Some people think they are dangerous. But they don't know tigers are in danger now. There are only 20 to 30 wild South China Tigers in China and less than 300 in the world. Lots of people kill them for their fur. We should take action to protect them.