Many people have dogs at home as pets. If a dog is happy, then he may want to meet you or play with you. If he doesn't feel happy, then he would rather stay alone. But dogs can't talk. How can you tell how your dog is feeling? By his body language.

    If your dog's head and back are lowered, his ears are down and his eyes are narrowed, and his tail is between his legs, then he is fearful. You may touch him gently to comfort him. If your dog's ears are up, his eyes are bright, and he wags his tail rapidly (快速地), he is very happy. He may also hold his mouth open more or even pant (气喘) mildly. Then you can go and play with him freely. If he closes his mouth and looks serious as you get closer, then he has changed his mind. It is better to leave him alone until he comes to you. Remember, we are talking about dogs that you know. Be sure a parent is around to allow you to get close to the dog. Get away from strange dogs even if they seem friendly.

    The most important clue (线索) is the mouth. If the dog's mouth is closed, then he is most likely to be not relaxed or happy, and he does not want you to touch or play with him right now.

    There is a lot of salt on the Earth, and it mixes very well with water.

There is some salt in all water. Water on the land runs into lakes and rivers. These rivers run into the seas and oceans. They carry a little salt with them. Some of the ocean water moves into the air and clouds. It evaporates. Salt cannot evaporate. It stays in the oceans.

    The water in the oceans has more salt than river water. There is about 3. 5% salt in the ocean water. Some seas have more salt than others.

    Some of the water leaves the lakes. It evaporates, but the salt cannot. These lakes are very salty. There are two famous lakes like this. They are the Dead Sea in the Middle East and the Great Salt Lake in Utah(犹他州）in the United States. They are much saltier than the Atlantic Ocean（大西洋）and the Pacific Ocean(太平洋）.

    What do you usually do on your smartphone? Send text messages, make phone calls or play video games? Now, thanks to a beginner-friendly programming（程序设计） tool, kids can do more than just play games on their smartphones-they can make their own games.

    US high school student Samuel Ndungi spent a few months learning how to make apps（应用软件）for smart-phones.

    "I was really shocked that you could do this on your own," Ndungi said "I thought only people from Microsoft and big companies could do this."

    Ndungi took a class run by his teacher, Michael Braun. In Braun's class, kids learned how to use the beginner-friendly programming tool to program their own mobile apps.

    This tool is called TouchDevelop. It puts basic instructions（基本指令） into blocks of code（代码）, and kids can put them together like Legos to run games, stories and other apps.

    With TouchDevelop, student Tony Huynh learned how to make his own games. "You get to put your own thoughts into the game, like the animals you want, the kinds of backgrounds you would like to see, and so on," he said.

    Another student Shina Williams wrote a program with about 80 lines of code that paints a picture of his childhood Teddy Bear." It's your own creativity, your own mark（印记） of something that's put in there and it stays in there, " she said.

    Coding is more than just a job skill. Children who learn coding also find new ways to think, create and express themselves.

    Do you know what makes lightning (闪电)? {#blank#}1{#/blank#}

    Lightning strikes happen when ice and water in clouds rub (摩擦) together, and cause atmospheric (大气层的) changes. When this happens, it creates a static charge (静电). Lightning can strike inside the cloud, between two clouds or between a cloud and the earth. {#blank#}2{#/blank#}

    Lightning can be very dangerous. Every year, lightning kills people because it can start big fires or because it reaches a temperature of 28,000℃. About 1,000 people are hit by lightning every year in the United States, and about 100 of them die as a result.

    {#blank#}3{#/blank#}Scientists think that there are more than three million lightning strikes every day in the world. An American man, Roy Sullivan, who worked in a park, survived from the most lightning strikes. {#blank#}4{#/blank#}And he keeps the highest world record.

    Lightning is sure not something to play with. When lightning strikes, it's best to stay inside a large building. {#blank#}5{#/blank#}Also, do not lie down on the ground, or the electricity may go through you and cause a heart problem.

There are many colors in nature. But do you think that a color has weight? Let's do a test.

First, put two objects with the {#blank#}1{#/blank#} weight into two boxes. Then cover the boxes. Third, wrap (包裹) one box with a red piece of paper, the other with white. Now hold the boxes {#blank#}2{#/blank#} your hand one by one. Which one is {#blank#}3{#/blank#} ? It is certain that you will think the red one is heavier. Why do you think so? A scientist did many {#blank#}4{#/blank#} and found that different colors have different weights in a man's mind.

Also, scientists say that people accept the colors they like, and {#blank#}5{#/blank#} the colors they hate. So your body and mind will be {#blank#}6{#/blank#} by using the colors you like. Or you'll be nervous {#blank#}7{#/blank#} even get ill. For example, you {#blank#}8{#/blank#} blue and hate red. If you stay in a room with red windows and wallpaper for two hours, you'll feel you have been there for {#blank#}9{#/blank#} hours. But if the room is blue, you'll feel you have been there for only an hour, And, if a person walks {#blank#}10{#/blank#} of a blue room and into a red room, his temperature will rise. That means our body temperature will change with different colors.

Many social media posts(社交媒体帖子) may let you believe that everyone is happy all the time, but being happy all the time is not possible.

As a teenager, you probably expected to get good grades in an exam or to win the most important basketball game, but it didn't happen. Good results make you happy and bad results make you sad. But sadness can drive you to improve yourself next time.

However, when people get into sadness for a long time and it starts to affect(影响) their lives, it's called depression (抑郁). You don't want to get out of bed. You don't feel like studýing or going out with your friends. I remember the same feeling when my dog Rebel died in an accident. I remember that he followed me to school. Now he was gone, and I lost all interests to do anything.

My parents told me dogs don't live forever. What was more, Rebel had a good life. If Ihad a good life, Rebel must be happy, too.

Depression is not a person's mistake. It's normal to feel sad sometimes. Many great people, like the comedy actor Jim Carrey, once get depressed. But you should know what to do to stop depression or make yourself less depressed.

When you feel down, you must not keep yourself away from the world. Try to share your feelings with a family member or a good friend. Staying at home by yourself will make you more lonely. You should stand up, open the window, and throw away (抛弃) the sadness.