B

    Many years ago, there was a very popular sport in America. Who invented the sport more than 3,000 years ago? We don't know. But everyone thinks it was the Olmecs(奥梅克人）made it popular.

    People don't have the same rules about the game all over the world. People in different parts of the world play the game in different places at different times. If we want to bring back the sport, we need to have two teams of players standing on each end of a court. When the game begins, the two teams need to pass a ball from one side of the court to the other. The players can't touch(触) the ball with their hands and feet. But they can use their elbows(肘) and other parts of their bodies hit it. If a player does not pick up the ball in time and lets it fall to the ground, that team loses a point. But if a player makes the ball through a hoop(环),that team scores a point. The team with the most points wins the game.

    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 mall might have thrown the dish away. But Fleming was very careful and smart. He understood what the mold did. How lucky the humans were!

    Scientists found that moderate (适度的) noise can make people more creative, The New York Times reported.

    Scientists did tests on students. They divided them into four groups. They then asked the students to do certain tasks involving creative thinking. But each group did the task with different volumes (音量) of background noise. They found that students did best when working under moderate noise—70 decibels (分贝). This is about the same volume of background noise in a cafe. Students did worse in low noise (50 dB). This is the volume of a quiet room. They did the poorest when in a high-noise (85 dB) environment. This is the noise level in a factory.

    Moderate noise can distract (分心) people just enough so that they think more creatively. "It helps you think outside the box," Raci Mehta, a lead researcher in the study, said to the Business Standard. On the one hand, working in a very quiet place can strengthen our focus. But it also stops

    us from thinking abstractly (抽象).

    "This is why if you are too focused on a problem and you can't solve it," said Mehta, "you leave it for some time and then come back to it and you'll get the solution."

    However, the scientists said that when you need to do detailed things, like proofreading (校对) a paper, a quiet place is better than a noisy one.

    When you look at the sky at night, the Moon looks bigger than the stars. Actually (实际上), the Moon is much smaller than the stars and the Sun. It's much smaller than the Earth. But the Moon is much closer to us than any star. That is why it looks so big. If you hold a coin close to your eyes, it looks big. If you look at it across the Moon, it looks small.

    The Moon moves around the Earth. It makes one trip in about four weeks. The Moon looks flat to us. But it is a round ball, like the Earth.

    People once thought the Moon had fire (火) on it. They thought the fire made it bright. Now we know the Moon is like a mirror. It gets its light from the Sun.

    Our sunlight comes from the Sun, too. What is the Sun? The Sun is a star. The stars we can see have their own light. There are many big stars we cannot see. Their light has burned out. Others are still bright, but they are so far away that we cannot see them. The Sun looks bigger and much brighter than other stars in Galaxy because it is the nearest of all stars. The Sun and the other stars we see are very hot, but the air around us saves us from the heat of the Sun.

    The Sun gives us light and warmth (温暖). It makes plants grow and turns leaves green. It makes life possible on the Earth. It is a life giving star.

    Now there is too much garbage(垃圾) on the earth. Our planet is in danger, so it is urgent(紧迫) to classify(分类) garbage. How should garbage be classified? The following pictures may help you.