The Renaissance，considered by modern scholars to have been the time between 1,300 and 1,600，was a period of European history when many new inventions and beliefs came into being.

    The Renaissance is traced back to rich Italian cities such as Florence，Milan，and Venice.In these cities businessmen started to spend their extra money on things like painting and education，and to consider new techniques of banking and systems of government.A new type of scholar，the humanist(人文主义者)arose.Humanism was concerned with humankind and culture.Latin and Greek，literature and philosophy，music and mathematics were among the subjects humanists studied.

    The Renaissance gave rise to new forms of painting and  sculpture.During  the  Renaissance，artists were no longer regarded as mere artisans(工匠)．Many artists drew on mathematics in order to become more accurate in their measurements(度量)and to make sure an object was presented in realistic proportions.They also studied the way light hits objects and the ways our eyes perceive it.A new kind of paint，called oil paint，was invented.

    The Renaissance affected all of the society.Many people became interested in politics，and the world outside their towns.They became explorers，businessmen，etc.The effect on religion was especially strong.In the Middle Ages people were primarily concerned with serving the church and getting to heaven.But the increase in arts  and education gave  people things to look forward to in life，and made them lose interest in the church.

    The  Renaissance  produced  many  great minds.Leonardo da Vinci was one of the greatest，although he was not regarded that way at the time.Among his many works of art were Mona Lisa and The Last Supper.He is also regarded as a great inventor，and is credited for coming up with the idea of the helicopter.

    You may have heard adults say they are uncomfortable in the morning without a cup of coffee. One reason they may feel that way is that coffee contains caffeine(咖啡因). Caffeine appears naturally in coffee, tea, and cocoa beans, which are used to make chocolate. But now food makers are adding it to many products, from potato chips to water.

    The US government is especially worried about the problem. That's why the Food and Drug Administration (FDA) is studying the health effects of caffeine on young people. Studies show that too much caffeine can make people nervous and unable to sleep. What's more, caffeine is habit-forming. Those who consume it regularly and stop suddenly may experience headaches and feel tired.

    One of the biggest concerns is the large amount of caffeine added to so-called energy drinks, like Red Bull. A 12-ounce can of cola has about 35 milligrams of caffeine. A similar serving of Red Bull contains more than three times that amount.

    The Institute of Medicine is also working on caffeine-safety measures. “Teenagers should not drink beverages that contain caffeine. They should be aware of caffeine's effects on health and on how the brain works. Take, for example, teenagers who consume caffeine to stay awake and study for a test. They will remember less of what they just studied,” said Stallings, a member of the institute.

    Companies that make products with added caffeine claim they do not advertise them to kids. However, there is no law to stop children from buying them. So the FDA needs to set limits on caffeine, especially in energy drinks. As for added caffeine in foods, the government should just say no. If not, the amount of caffeine should be printed on food labels to remind consumers. The government must do that.

    Doctors say kids should avoid caffeine. If you need extra energy, try these natural boosters: eat right, exercise, and get plenty of sleep.

    We all know what a brain is. A doctor will tell you that the brain is the organ of the body in the head. It controls our body's functions, movements, emotions and thoughts. But a brain can mean so much more.

    A brain can also simply be a smart person. If a person is called brainy, he is smart and intelligent. If a family has many children but one of them is super smart, you could say, “He's the brains in the family.” And if you are the brains behind something, you are responsible for developing or organizing something. For example, Bill Gates is the brains behind Microsoft.

    Brain trust is a group of experts who give advice. Word experts say the phrase “brain trust” became popular when Franklin D. Roosevelt first ran for president in 1932. Several professors gave him advice on social and political issues（问题）facing the U.S. These professors were called his “brain trust”.

    These ways we use the word “brain” all make sense. But other ways we use the word are not so easy to understand. For example, to understand the next brain expression, you first need to know the word “drain”. As a verb, to drain means to remove something by letting it flew away. So a brain drain may sound like a disease where the brain flows out of the ears. But, brain drain is when a country's most educated people leave their countries to live in another. The brains are, sort of, draining out of the country.

    However, if people are responsible for a great idea, you could say they brainstormed it. Here, brainstorm is not an act of weather. It is a process of thinking creatively about a complex topic. For example, business leaders may use brainstorming to create new products, and government leaders may brainstorm to solve problems.

    If people are brainwashed, it does not mean their brains are nice and clean. To brainwash means to make some accept new beliefs by using repeated pressure in a forceful or tricky way. Keep in mind that brainwash is never used in a positive way.

    Are some people born clever, and others born stupid? Or is intelligence developed by our environment and our experience? Strangely enough, the answer to these questions is yes. To some degree our intelligence is given to us at birth, and no amount of education can make a genius out of a child born with low intelligence. On the other hand, a child who lives in a boring environment will develop his intelligence less than one who lives in rich and varied surroundings. Thus the limits of person's intelligence are fixed at birth, whether or not he reaches those limits will depend on his environment. This view, now held by most experts, can be supported in a number of ways.

    It is easy to show that intelligence is to some degree something we are born with. The closer the blood relationship between two people, the closer they are likely to be intelligent. Thus if we take two unrelated people at random from population, it is likely that their degree of intelligence will be completely different. If, on the other hand, we take two identical twins, they will very likely be as intelligent as each other. Relations like brothers and sisters, parents and children, usually have similar intelligence, and this clearly suggests that intelligence depends on birth. Imagine now that we take two identical twins and put them in different environments. We might send one, for example, to a university and the other to a factory where the work is boring. We would soon find differences in intelligence developing, and this indicates that environment as well as birth plays a part. This conclusion is also suggested by the fact that people who live in close contact with each other, but who are not related at all are likely to have similar degree of intelligence.

    Most people will answer a ringing phone. Usually you don't know who is phoning or how urgent their business is, so a ringing phone is difficult to ignore. In one experiment, a researcher wrote down the numbers of several public phones in stations and airports. Then he called the numbers. Someone nearly always answered. When he asked why, people usually said, "Because it rang."

    A few years ago in New Jersey, a man with a rifle killed 13 people. Armed police surrounded his house but he refused to come out. A reporter found out the phone number of the house and called.

    The man put down his rifle(步枪) and answered the phone. "What do you want?" he said, "I'm really busy right now."

    Imagine you're at work and the phone is ringing in someone else's office. Do you answer it or not?

    In one survey on telephone use, 51% of participants told researches that they did. We can't ignore the phone and for the reason, it forces its way into our lives. It interrupts what we are doing and on top of that, the caller is often someone we don't really want to talk to. However, in the survey, 58% said they never took the phone off the hook, and 67% didn't mind if someone called during a television programme. For 44% it wasn't a problem if someone rang during a meal, while only 28% were annoyed or upset.

    If someone phoned in the middle of the night, 40% told researchers that they got nervous or frightened, while around 30% got angry.

    Of course, when someone is really annoying, you can choose to hang up on him/her. This is in fact one of the rudest things you can do on the phone, but 79% said they were prepared to do it in some cases. Only 6% told researchers they never hung up on people.

    City trees grow faster and die younger than trees in rural forestry, a new study finds. Over their lifetimes, then, urban trees will likely absorb less CO₂ from the air than forest trees.

    As we all know, the earth would be freezing or burning hot without CO₂. However, CO₂ is a greenhouse gas, meaning it traps energy from the sun as/heat. That makes temperatures near the ground rise. Human activities, especially the widespread burning-of fossil(化石)fuels, have been sending extra greenhouse gases into the air. This has led to a rise in average temperatures across the globe.

    Studies had shown forests readily absorb CO₂, but there hadn't been much data on whether city trees grow, die and absorb CO₂ at the same rate as forest trees do. So some researchers decided to find out.

    To figure out how quickly trees were growing, researchers tracked their diameters (the width of their trunks) between 2005 and 2014. A tree's diameter increases as it grows, just as a person's waist size increases as they gain weight. About half the weight of a tree is carbon, research has shown. Most of the rest is water. Over the nine years' tracking, the researchers found city trees absorbed four times as much carbon from the air as forest trees. However, they were twice as likely to die. So over the lifetime of each type of tree, forest trees actually absorbed more CO₂.

    City trees grew faster because they had less competition for light from their neighbors. In a forest，trees tend to grow close together，shading their neighbors. Street trees also benefit from higher levels of nitrogen (氮)in rainwater. Nitrogen helps plants grow. Waste gases from gas-burning cars also contain nitrogen, thus enriching city air with nitrogen. Later, rainwater may wash much of it to the ground. Some street trees may also have better access to water than trees in the country because the underground water pipes can leak.