Bats are the only “flying animals” in the world. They can't see very well. We often hear “as blind as a bat”. Yet they have no trouble flying on the darkest nights and finding their ways round. How can bats fly and see at night? They fly by radar(雷达).

The bat's radar system(系统) works the same way as the radar in ships and planes. As a bat flies through the air, it makes a sound. If the sound hits things, it will come back and the bat's ears will receive the message. In this way the bat is able to know where the things are. Bats go out for food at night. In the daytime they hang in some dark places. Some people think bats are bad animals. In fact they are useful animals.

    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 four 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 smartphone 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 security（安全）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. 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.

    What was discovered by accident? The answer is penicillin (青霉素). It kills germs. By killing germs, it saves lives. Suppose you are sick. You go to a doctor. She examines you. She says you have a "staph" infection (葡萄球菌感染). She gives you some medicine. You take it. The medicine knocks out the staph. Soon you are well. Before penicillin, this would not happen. Staph was almost sure death.

    Everyone wanted a medicine. Laboratories worked day and night. They grew the staph in small dishes. Then they tried to kill it. Nothing worked.

    The laboratory dishes had covers on them. They kept things from falling into dishes. Molds (霉菌) were a big worry. They are always in the air. You can't see them. They're too small. There are thousands of different molds. Molds can make an experiment fail. That's why dishes are covered.

    Dr. Alexander Fleming was working to kill the staph germ. He worked for years. One day he took a cover off a dish. He looked inside. There was a thick growth of staph germ. There was also some mold. Then he saw something strange. Where the mold was, there was no growth of staph. This is what Fleming probably thought. "By accident, I found a mold to kill the dreaded staph."

    This is how penicillin was found. But here's the real miracle. There are thousands of kinds of molds. But only one kind can kill staph. The mold must have fallen into the dish a few days before. The cover was probably off only a few seconds. In those few seconds the right mold fell into the right dish. Another man might have thrown the dish away. But Fleming was very careful and smart. He understood what the mold did. How lucky the humans were!

    Every year on 15th October, over 200 million people around the world take part in Global Handwashing Day. But why do we have a day for something we do all the time? Well, research shows that not enough people often wash their hands with soap. Experts believe that this leads to the deaths of millions of people every year.

    Sidibe, a public health expert says soap is the most beautiful invention in public health. Washing your hands with soap can have a huge impact on reducing (减少) the spread of diseases. Handwashing with soap prevents babies from getting ill and keeps children healthy in school.

    However, washing hands with soap does not happen as often as you might think. This is partly because there aren't enough resources (资源) in poorer countries, but it's also because for many people, handwashing is simply not part of their everyday life. It's not easy to get people to change habits they learned in early childhood -- but this is what Global Handwashing Day wants to do.

    In 2008, the Indian cricket team joined around 100 million Indian schoolchildren in washing their hands to promote (促进) the first ever Global Handwashing Day. Every year since then, many different events have been held around the world. In 2014, Global Handwashing Day was used in the fight against Ebola, a very serious disease, with events held in affected (受感染的) African countries.

    Today, local and national leaders continue to use the day to spread the message about the importance of clean hands. The hope is that handwashing becomes a necessary part of people's lives and improves the health of millions around the world.

    A black hole is a place in outer space with very strong gravity. Gravity is a great force(力量) that shapes the universe. On Earth, gravity makes apples fall from trees. It keeps your feet planted on the ground. The gravity in a black hole is much stronger. It is so strong that nothing around it can get away from it, not even light.

    Black holes are invisible. We can't actually see them because they don't throw back light. But scientists can find them with space telescopes(望远镜)and special tools. The strong gravity makes nearby stars move in a certain way. By studying how the stars move, scientists can find out if they are flying around a black hole. Strange things happen around black holes. This makes black holes a popular subject of science fiction(科幻)stories, although they are very real.

    A black hole forms when a star dies. The star falls in on itself and turns into a very small point. Because of its small size and huge mass(质量), the gravity will be so strong that it will pull light in and become a black hole. Black holes can grow huge as they continue to pull other things in and "eat" them. Many scientists believe that there are super-massive black holes at the center of galaxies, including the Milky Way.

    The idea of the black hole was first suggested by two different scientists in the 18th century: John Michelle and Pierre-Simon Laplace. In 1967, a physicist named John Archibald Wheeler came up with the name “black hole". Studying black holes can tell us many things about our galaxy and help scientists answer questions about the universe.