【推荐1】What did people do to communicate in ancient times? Here are some very interesting answers to this question.

Alphorns (阿尔卑斯长号角) were once used to communicate in the mountains in Switzerland. They are very long and they are very heavy, too. So, alphorns are hard work to blow. Then why use them? Well, they make a loud sound which travels much further than the human voice. Herdsmen (牧民) used them to call cows in the distance (在远处) for milking. At sunset, alphorns were also used to send a message down to villagers that all was well. These days, they’re mostly used as musical instruments.

The people of La Gomera, an island in Europe, have their own special way of sending messages from mountain to mountain. They use a whistled (口哨的) language called el silbo. El silbo comes from their language Spanish. Whistling can be heard within five kilometers, so it can be used across much greater distances than shouting. El silbo can be used for all kinds of messages, including greetings and announcements. El silbo is used a lot less than it used to be, but primary school students in La Gomera have to learn it.

Did you know it’s also possible to send messages without making a noise? This is called visual (视觉的) communication, and it includes the use of flags and even smoke. Long ago, soldiers along the Great Wall of China used smoke as a warning. If they noticed the enemy from their signal (信号) tower, they lit a smoky fire. When soldiers in other towers saw the smoke signal, they lit fires, too. In this way, messages about the enemy’s arrival could travel as far as 800 kilometers in just a few hours.

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【推荐2】Have you ever poured water onto your shirt carelessly? Usually, clothes darken in color when they get wet. Why do clothes often appear darker when they get wet?

Before understanding this question, we should first take a quick look at how we “see” colors. Take a red shirt as an example. When it is hit by the light from the sun, it absorbs (吸收) different wavelengths (波长) of light, except for the red light wavelength. The red light wavelength is reflected (反射) to our eyes. That is why the shirt appears red to us.

Now let’s return to the wet shirt. When the light hits a wet shirt, it has to pass through the water on the shirt. The light that should be reflected by the shirt is re-absorbed by the water. This means less light will be sent to our eyes. As a result, the shirt looks “darker”.

But remember, sometimes a wet shirt can seem brighter from some special angles (角度). The surface of a shirt is usually rough (粗糙的). Adding water to it makes it smoother. A smooth surface reflects light in a different way from a rough surface. So you may see a small and bright reflection of the light from a certain angle. So basically, a wet shirt will be darker than a dry one, but it can also appear more “shiny” at times.

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【推荐3】①Large dying stars form a black hole. The black hole can “eat” anything that comes too close and even light can’t get out of it.

②Scientists from Harvard University recently said that in 2018, a black hole named AT2018hyz ate a small star. The black hole is 665 million light-years from the earth.

③Now, the same black hole has become active again. This time, it has been ejecting (喷射) the things it ate at half the speed (速度) of light. “This caught us completely by surprise—no one has ever seen anything like this before”, said a scientist.

④When a black hole eats a star, it may throw back some pieces of the star into the universe. The whole event is called a Tidal Disruption Event (TDE, 潮汐撕裂事件). A common TDE usually happens immediately after the “eating”. However, the black hole, AT2018hyz, threw back the things it ate three years later.

⑤The scientists thought about the possible reasons (原因) behind the event. They first turned to the density theory (密度理论). If the density is very high around the black hole, an ejection might happen. Another reason might be that the other TDEs were happening, but scientists could not see them from the earth. However, scientists have not yet found the true reason.

【推荐2】When you wake up every morning, you need to decide what to wear, what to eat, where to go etc. Along the road of life, you make many decisions. So you should be cautious（谨慎的）about decision making.

Ken Levine said, “We all make decisions, but in the end, our decisions make us.” You can’t ignore the importance of decision making. Even one small choice can make a huge difference. However, for every choice, big or small, it’s not easy to make the right decision. Here is some advice for you.

※Don’t make decisions when you are over-excited, angry, or sad. Riding high on emotions（情绪高涨）can influence your ability to make a good decision. If you can’t stay cool, put off making the decision until you’re thinking clearly.

※Most decisions are made better when you have enough information. Do some research to find out as much as you can about your decision.

※There are usually many choices for you, so try to make a list of all the choices. And don’t make decisions until you’ve got a full list of your choices. If you have trouble thinking of all the choices, ask your family or friends for help.

※The best way to make a decision is to think about how you’re going to feel about it in the future. WarrenBuffett’s 10/10/10 Rule can help you make decisions. It’s really simple and you just need to remember the three questions: How will you feel about your decision in 10 minutes? How about in 10 months? How about in 10 years?

Of course, if you finally find out that the decision is wrong, remember that life hand you lemons sometimes.