Do you know how many pandas there are in the world? World Wildlife Fund (WWF) has spent four yours counting pandas in the world. It says there are 1,590 now. In the 1980s, there were only 1,100.

So we may say that pandas are lucky because people around the world love them and are trying their best to help them. However, we also say that pandas are unlucky because they are still facing a lot of problems now.

Pandas are not good at making babies. Even in the wild, scientists have found that female pandas give birth only every 28 months. That's why the number of pandas goes up so slowly.

Pandas need bamboos for food, but bamboo dies every 10 to 100 years. It can take up to 20 years to provide(提供) food for pandas. When bamboo dies, pandas have to move to other areas. In the past, this was easy. However, the number of people keeps growing, people cut down more forests and built more villages. It's more difficult for pandas to find bamboos and homes than before.

In the past years, WWF made great efforts to protect pandas. And some Chinese scientists are also always trying to find ways to help pandas.

    On April 2, we said goodbye to Tiangong I, China's first space lab. According to the China Manned Space Agency (中国载人航天), Tiangong I re-entered the Earth's atmosphere (大气层) and some of its debris (碎片) fell into the South Pacific Ocean.

    There are many spacecraft (宇宙飞船) that are still in orbit(轨道) above the Earth. After finishing their trips, they will all re-enter the Earth's atmosphere like Tiangong I.

    There are two types of re-entries: controlled re-entry and uncontrolled re-entry.

    Some satellites and manned spacecraft come back to the Earth in a controlled re-entry. Experts calculate (计算) the path of the falling spacecraft and its speed. Thy can guide the spacecraft to fall in a chosen area.

    Some spacecraft may have problems while in space after a certain amount of time. These spacecraft come back in an uncontrolled re-entry. It is hard to tell when and where these spacecraft will fall until the last few hours. The US space station Skylab came back partially uncontrolled in 1979. Parts of the station fell in western Australia, but no one was hurt.

    During re-entry, most of the spacecraft will burn up while passing through the Earth's atmosphere. Only a small amount of the debris will reach the ground. The debris typically ends up falling into the ocean, China Daily reported.

    Today is December 15, 2030. Influenced by the launch of the first manned mission to Mars next month, you will most likely get a gift card for a space trip.

    The interest in trips, 100km above the surface of the Earth, has grown steadily since such a trip began. However, the market has grown much larger this year since the official announcement of the Mars mission. More low - cost spacelines have entered the market and you can now find flights for such a trip for as low as $3,495.It's very reasonable.

    Space tourism( 旅游业，观光业) is one of the markets that have developed fast during the last decade, with the opening of the Starbright Hotel on the moon as well as the low orbital hotels that started accepting guests. However, accommodation in space is still expensive for the average household, so the suborbital (亚轨道的) flights with thirty - minute weightlessness during the three - hour flight will for some time be the most popular trip.

    However, the spacelines might in the future face fierce competition between space elevators (太空升降舱), like the one that is projected to start construction within two years. Once it is fully functional, it will start to ship cargo to space. But it will accept passengers as soon as possible to get back the large investment. Even if the elevator becomes successful, it will take several years before there are more elevators in the world to get in the competition for space traffic with the spacelines.

    Those who are looking for a little bit of adventure and have extra money to spend may want to consider a suborbital flight in space. While a suborbital flight may not be the space mission that you have always dreamed of, it will give you the rare opportunity to see what our planet looks like in a high - altitude flight outside our atmosl3here. So before you enjoy a trip by elevator to space, enjoy a suborbital flight first.

    "What? You too? I thought I was the only one." Have you ever said to someone? If so, you may have ended up becoming friends.

    It seems that similarity often helps form a friendship. Aristotle once said, "Some define (给……下定义) it (friendship) as a matter of similarity; they say that we love those who are like ourselves."

    Now, there are some scientific explanations for this idea. The scientists from the University of California said friends have similar brains, Scientific American reported.

    The scientists invited 42 university students to take part in a scientific test. Each student watched the same set of videos. At the same time, the scientists scanned (扫描) their brains and recorded their brain activities.

    According to their study, friends who watched the same videos reacted (反应) in similar ways. Similar parts of their brains lit up while watching the videos, especially the parts that were connected with motivation, learning and memory. However, people who weren't friends had different reactions to the same videos.

    "Having close friends whose brains react like ours may be rewarding because it reinforces (加强) one's own values, opinions and interests," lead scientist Carolyn Parkinson told Business Insider.

    But brain similarity is not the only thing that can result in a friendship. Scientists from the University of Leipzig, Germany, found that a friendship is also based on how physically close you are to someone. They did a scientific test on first-year college students who met in class for the first time. In this test, students who sat next to each other were more likely to become friends.

    What is the best way to help control air pollution in our towns and cities? Choose public transportation instead of private cars, or reduce the total amount of cars on the street. These can be useful. But here is a more creative way—write a poem.

    "I write in praise of air. I was six or five, when a magician opened my fist(拳头), and I held in my hand the whole of the sky."

    Professor Tony Ryan (the science expert) and Professor Simon Armitage(the words expert), from the University of Sheffield, UK, came up with the idea.

    But in fact, the poem is not the key part. It is the poster that the poem was written on that plays the biggest part. The poster is 10 meters by 20 meters. It is coated with nanoparticles(纳米粒) of titanium dioxide (二氧化钛). It can absorb the waste from around 20 cars each day if you put it by a busy road. The poster is now displayed on one of the University of Sheffield's buildings.

    It doesn't get rid of all the pollutants from traffic, but it will eat up things called nitrogen oxides (氧化氮). These play a part in breathing problems, including asthma(哮喘).

    The technology is cheap. "It would add less than £100 to the cost of a poster and would turn advertisements into catalysts(催化剂) in more ways than one," Ryan told the BBC.

    He's also working on another idea, which is to add the nanoparticles to washing powder, so that your clothes soak up these poisons while you walk along. And you wouldn't be able to see or feel anything different.