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 (实验) 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 (奇迹). 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 (秒). 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!

    How do you pay for your meals at a fast food restaurant? With change(零钱)? Nowadays we have We Chat wallet and Alipay.

    I use my tap-and-go card(感应式信用卡). I don't even need to enter my PIN number(SIM卡密码)or a signature(签名)to pay money. It's quicker and everybody in the queue(队)is happy.

    Contactless payments(非接触式支付)are more and more popular, but the safety (安全性)still needs improving(改善). And people shouldn't pay too much at a time-in the UK it's ￡30. If you use the card a few times, you will need your PIN number.

    Some things, such as your clothes, have been combined with electric technology(与电子技术联系起来). Kenneth Cukier, the writer of the book Big Data, says, "You can take any card and put it in a coat. When you make a payment, just wave your arm in front of the terminal(终端)." This is for people who don't want to take their card out of their pocket, or use their phone or watch.

    Good, isn't it?

    So spending money is becoming easier at the time. And people are buying more and more things. But making money still needs the hard work.

    Back to work then!

    In the universe, as we all know, there is the Sun, the Moon, the Earth and a good many stars. Through our geography lessons, we know the Earth goes around the Sun, and the Moon goes around the Earth. We have day and night because the Earth keeps turning all the time. When our part of the Earth turns to the Sun, it is day. When our part of the Earth turns away from the Sun, it is night.

    Just because the Moon is closer to the Earth than the Sun, it looks much bigger than the Sun. Big things will look smaller when they are further, and small things also look bigger when they are nearer.

    The Sun is big enough to give out very strong light. The Moon can't give out any light at all, but it looks quite bright, too. Why? In fact, the light from the Moon comes from the Sun. The Moon looks much bigger and brighter than the stars. But actually the stars are much bigger and brighter than the Moon. They look smaller than the Moon also because they are farther away from the Earth.

    There are many other planets in the universe. But of all the planets, only on the Earth there are living things and people can only live on the Earth, too. But at 9: 00 a. m. on October 15th, 2003, Chinese pilot Yang Liwei was sent up to space. He stayed there for over 21 hours. It was the first time for Chinese to get into space.

    China's first artificial intelligence (AI) textbook series designed for primary and secondary school students is expected to be introduced into hundreds of campuses across the country in 2019. The textbooks will be used for elective courses or as part of school﹣based curriculums.

    Significant progress is being reported in China in AI technological research and development, with authorities now moving to promote AI﹣related education.

    According to the publisher, East China Normal University Press, the series will have 10 volumes, with six volumes published so far. Each has its own theme, with 12 to 14 main chapters and 2 to 4 chapters of activities. This series covers the educational demands of students from primary school to high school on AI and provides a systematic framework of AI knowledge.

    The books have been used in three schools in Shanghai as a pilot program and well received by students, according to Wang Jiqing, chief editor of the series.

    Populations of white-tailed deer(白尾鹿) are growing rapidly in many parts of the United States. As populations grow, food becomes a problem. Many deer die of hunger. Others grow up small and unhealthy. In search of food, hungry deer move closer to where humans live. They eat farm crops, vegetables and even trees. Besides, increased numbers of deer near roads can cause traffic accidents.

    People admire the grace and fast speed of deer. Most people don't want these animals to be hungry and ill. Should people take action to control the growing deer populations?

Should People Take Direct Action?

    Many people think that hunting(打猎) is the best way to control the animal populations. Wildlife managers will see if there's enough food in an area and decide its carrying capacity(容量). Then hunters with licenses are sent to help control the number of deer. Hunting is usually not allowed in cities or suburbs, however.

    Some people have the idea to catch the deer and move them to other places. But this method is expensive and requires finding another place that can accept the deer without breaking the balance of ecosystem(生态系统).

    Scientists are also working to develop chemicals(化学药品) to control the birth rate(率) in deer populations. But this plan works for only one year at a time.

Should People Take Indirect Action?

    Some suggest bringing in natural enemies of deer, such as wolves, lions and bears, to areas with too many deer. But these animals could also hurt dogs, cats, and even humans. Other communities have built tall fences(篱笆) around areas to keep out the deer. However, this is impossible for farmers.

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    Some people are against any kind of action. They support leaving the deer alone. Animal populations in an area naturally go up and down over time. Doing nothing means that some deer will die of hunger or illness. But finally, the population will reach a size within the carrying capacity(容量) of the environment. So, let nature go its own way.