1 . Many people post (发帖) very often, especially teenagers don’t think before they post. So they post a thought they think is funny or a photo or video they feel good about. Within seconds, the whole world can see what they’ve posted. Most of the time this isn’t a problem but here are 3 things for teenagers to consider before posting on social media (社交媒体) in order not to make a mistake.

1.Who will read it?

Any time we post something there is possibility for that post to go viral (疯传). You need to be clear that there is no private on the Internet. You should know that all your friends, teachers, families and any people you may never meet can (and might) see everything you post.

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Before posting, you need to consider the people who may read the post or hear about it. Will the post make anyone feel comfortable? Will it hurt someone’s feelings? Will it make someone feel unsafe?

3.How does it represent (代表) you?

When you post you are sending out a representation of yourself. You need to realize that you will be judged (评判) because of your posts. When your posts include pictures or videos, you will be judged on superficial (表面的) parts of the posts including how you look, and the clothes you wear. You’ll also be judged on your ideas about social problems.

So, before posting, you should take a moment to look over the post and consider whether it’s proper. If you aren’t sure, you should probably remember: when in doubt, don’t post.

5 . On Dec. 9, 2021, three Chinese astronauts gave a science lecture 400 kilometers above Earth. Zhai Zhigang, Wang Yaping and Ye Guangfu, who are working abroad the Tiangong space station, showed millions of students their life there. They also did some fun science experiments. Let’s take a look at some of them.

Use it or lose it

The human body grows with the pull of Earth’s gravity. But in space, our bones and muscles don’t need to sustain our body’s weight. This will cause bone and muscle loss. NASA says that astronauts can lose up to 20 percent of their muscles after just a couple of weeks. That is dangerous because they will be too weak to work.

Astronauts have different ways to prevent this. During the lecture, Zhai introduced a special uniform Ye was wearing. It’s called a “penguin suit”. There are many elastic bands inside the suit. Wearing it, astronauts use their muscles to stretch the bands. This keeps their muscles strong.

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During another experiment, Wang made a water film. Then she added more water drops onto the film to make it a water ball. This can never happen on Earth. Why?

We need to first understand the surface tension of water. It is like a “skin” of water. The “skin” is there because water molecules are drawn to each other. Most of the time, gravity is too strong and it breaks the “skin”. But with zero gravity in space, the “skin” stays strong and the water ball will not break.

Water in space acts differently from water on Earth in other ways. For example, water will not flow downward if you try to pour it into a cup. That’s why astronauts usually drink water through straws in sealed bags.

Fights at school sometimes happen. But how can you keep away from (远离) a fight? Here’s something you can do.

Be calm (冷静). Sometimes, you feel so angry that you really want to teach somebody a lesson. But being angry can’t solve (解决) problems. Instead, it may bring you more problems. In the school, if anyone joins in a fight, the teacher will punish all these students. There are no winners in a fight.

Shout loudly. If you know a student is coming up behind you to attack (攻击), turn toward him, with your hands up in front of your body and loudly say “stop”. Loud voice can usually make the attacker to be calm. If he doesn’t stop, cry for help by calling out the name of a teacher.

Learn to say no. Your friend may ask you to join in a fight. Don’t do that. Helping him fight is not really helpful to him. If you really want to help him, try to ask him to give it up. Then, try to learn why he wants a fight and help him find a right way to deal with the problem.

7 . Every year, as the summer days grow shorter, an amazing change happens in Canadian forests. As summer changes to autumn, the trees turn colors, changing from summer greens to shades of red, orange, and yellow. It’s a truly wonderful sight! From a distance, the forest looks as if it’s on fire.

When I was a child, my grandmother told me that a strange little man came at night with a paint brush to paint the leaves those wonderful colors. And I believed her for it was a wonderful way of explaining this change to a little boy. But as I grew older, my natural curiosity led me to do some research on my own. As always, science had the answer.

Trees need food, just like all lives. Leaves produce food for the tree. It’s just sugar, which is sometimes called glucose (葡萄糖). Leaves use sunlight to change water and CO₂ into oxygen (氧气). The process by which leaves do this is known as photo-synthesis (光合作用). A chemical called chlorophyll (叶绿素) helps make this happen. Chlorophyll is the reason why leaves are green summer.

However, Canadian winters are long, cold and dark. There isn’t enough sunshine in winter for the leaves to make food. In autumn, as the days shorten, the trees get a signal to slow down. It’s time to take a rest. Don’t worry, though. They have enough food prepared to last all winter.

When the leaves stop making food, they no longer need to make chlorophyll. Slowly, the chlorophyll disappears. Remember, this is the chemical that makes leaves green. As the chlorophyll goes away, so does the green color. We begin to see the other colors that are always there. We could not see them before because green is a strong color.

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8 . The World Health Organization (WHO) says that 80% of the world’s teenagers don’t get enough exercise to live healthy lives. It did research (研究) on students aged from 11 to 17 in 146 countries for about eight years and got the result.

Doctors say 60 minutes of exercise a day is important for teenagers to build up their strength (力量). It’s also good for the heart and lungs (心肺). Also, teenagers won’t become fat through exercise. What’s more, more and more research is showing that exercise doesn’t just help with the body. It can help with the mind, too—making people think better and helping students get good grades.

Trevor Shilton working for the Heart Foundation in Australia says that doing exercise is really important, and he also says: “If this were a medicine, we would all take it.”

However, it’s not easy. Now many teenagers find it very difficult to stay away from smartphones, computers or televisions. In their free time, they talk with friends online, play online games and watch interesting TV programs. The WHO says that young people need to play less in the online world and play more in the real world.

Health experts want schools and families to ask teenagers to do more exercise. Doctors also say that teens can do 20 minutes of exercise three times a day to get 60 minutes of exercise. They say it’s very important for young people to do exercise, because it will be good for their lives in the future.

9 . On Nov. 20, a police dog training center in Beijing welcomes six new members. They are all cloned（克隆）dogs, China Daily reported.

The dogs were born in August. They were cloned from two police dogs who have helped police solve murder cases（谋杀案）.

Early this year, scientists took some cells from the dog’s skin and created cloned embryos（胚胎）. Then they put the embryos into three mother dogs. One mother gave birth to four dogs, while the other two gave birth to one each. The cloned dog’s DNA is a 99% match with their “fathers”.

It is hoped that the cloned dogs will be as talented as their “fathers” because they are cloned. The cloned dogs are just four months old, but have already shown that they’re brave and aggressive（有攻击力的）, as well as have great memories, according to Ma Jinlei, a police officer at the center. It will take less time and money to train them.

Kunxun, China’s first cloned dog, joined the police in Kunming in March. The world’s first cloned dog was born in South Korea in 2005.

However, animal cloning has long been a hot topic. The world’s first cloned animal, Dolly the sheep, died at the age of 6 in 2003, about six years earlier than most sheep. Some people have questioned whether cloning technology is safe.

In addition, some people worry that cloning technology may be used on humans someday and therefore may raise some problems. Can we call cloned human a real human?

10 . The blue whale (鲸) is the largest animal alive today. And one of these whales has been caught making a big journey through the South Pacific. The whale was first recorded near the Galapagos Islands, west of Costa Rica. Years later, that same whale was photographed off the coast of Chile in South America, a new study reports. The two places are separated by about 5,200 kilometers. That means the whale, nicknamed Isabella, swam farther than the distance between New York and Los Angeles.

Blue whales are found in all the world’s oceans but live in deep waters. So there are few places where they can be found easily. What’s more, they were nearly driven by whaling a century ago. Populations are increasing. But because there are so few of the animals, they are still considered endangered.

One blue whale may look like any other to the untrained eye. But each animal has special spots (斑点). “We use those spots as the fingerprints of blue whales,” Torres Florez says. To make the comparison job easier, scientists focus on the area around a whale’s dorsal fin (鳍), which is on its back. “Comparing those spots we are able to tell if a whale is the same whale we saw in different places or if the same whale is seen during different years in the same place,” he says.

Isabella is probably not the only blue whale to travel so far, the researchers say. Members of her population likely migrate regularly from Chile to the Galapagos. In summer months, Torres Florez notes, waters in the far southern Pacific are loaded with krill, but that food disappears in winter. That’s when the whales travel north to warm, tropical (热带的) waters near the Galapagos. There, instead of feeding, the whales produce babies. Scientists don’t yet know why whales prefer to produce babies in tropical locations. But the ocean there may be warmer and calmer and have fewer killer whales that would feed on baby blue whales, Torres Florez says.