The United States is a country of immigrants. It is a place where people from all over the world come to build a better life. Some immigrants bring their families. Some bring a few of their favorite things. Others come alone with nothing but determination. One thing that every immigrant brings with them is their culture.

    American immigration began in 1607 with the colony (殖民地) of Jamestown. In 1620, another group of people left England to build a settlement in America. They wanted to go to a place where they could practice their religion freely. Then many more people left their homes in Europe to build a better life in America. Many also came to America from Africa. By 1770, more than two million people had moved to America. Later on, more people came to the United States than ever before.

    In cities all over America, you can see different cultures that formed this country. Many things that you may think of as being “American” are actually from a foreign culture. Some of the best examples of this are the foods people eat. Pizza and spaghetti are foods that all Americans know and love. But both of them are from Italy. Baseball is an all-American sport. But the hot dogs that people eat during the game are a type of food that was brought to America by German immigrants.

    Over time, pizza and hot dogs have become a part of what is considered to be American food. In the same way, different groups of people have come together to define what an American is. An American can be a person of any background. An American can be of any faith. An American can be of any skin color. They can speak English clearly. They can speak English with an accent. Each new immigrant adds something new to American culture. It will keep changing as more people come to this country.

    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 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.

    Most people know that listening to music when they are feeling down or depressed can encourage their spirits.

    However studies have also shown that music, especially certain tones can reduce stress. Music can change brainwave patterns, deepen breathing, and bring on a totally stress-free and more open mindset（心态）. Using music to relax when considering a particular problem may not only raise your mood, but also could help you reach that "a-ha"moment and find a solution.

    Music has also been shown not only to make you feel good, but also, to be a great motivator. For example, during exercise, listening to music can keep you going, or get you to exercise more by helping you to ignore negative feelings of tiredness and focus on the pleasurable feelings you get from being absorbed in the music.

    Music is mainly used to record emotion. When we listen to a piece of music we share the artist's feelings on a visceral（本来的）level. That can be sad, and who among us hasn't put on a painful love song to share in the misery after a bad break-up? On the contrary, we can share in the delight of songs of joy and happiness, or any song or piece of music that reminds us of a particular happy time in our past.

    So next time you are feeling down, put on Beethoven' s Ode to Joy, I bet you will feel a lot better about whatever it was that was bothering you!

    To eat only a vegan（素食的） diet might sound difficult, especially with many popular dishes containing meat or other animal products. Yet in 2017, veganism was described as “the fastest - growing lifestyle movement” in the UK, according to BBC news.

    A study by a UK market research organization, suggests that over 542,000 Brits went vegan during the previous decade, an increase of 360%. And the main force behind this increase was those aged 15-34 years old — 42% of recent vegans fall under that age range.

    So why exactly has veganism become so popular among young Brits?

    One reason could be that many young people want to protect the environment, as less meat consumption is known to be beneficial to the environment. Global meat manufacturing is believed to cause 18% of the world's greenhouse gas emissions（排放）, even more than that of all the world's cars, trains and planes combined. Another reason is that many of today's young people believe that it's wrong to kill animals to be used as food.

    Jess Murray, 22, a student at University College London, said that he chose to become vegan after realizing that eating animals is a choice that people make, rather than something that we need to do to survive. “Becoming vegan was an ethical (道德的) decision,” he told the Guardian.

    Social media is also believed to have given rise to the increase in veganism. Platforms such as Facebook allow young vegans to connect with each other much easier, while others such as Instagram have led to the creation of “vegan celebrities (名人)”, who share lips on vegan lifestyles.

    Despite the rising of veganism, Laura Wyness, an expert in diet and nutrition, said that meat is very important for people's health. “A strict vegan diet makes it difficult to get some minerals and vitamins that your body needs,” Wyness told BBC news.

    However, the popularity of veganism doesn't seem to be fading. “It feels more like this is something that is sticking.” said an expert of the Vegan Society, a UK charity that promotes veganism.

    As most people know, in the last few years, sandstorms have swept across many cities and areas of North China, polluting the air and disturbing daily lives of human beings. People look dirty and suffer many kinds of illnesses, such as breath difficulty. The sandstorm is such a serious problem that it has not only weakened the industrial and agricultural development of our country but also caused a lot of trouble to the living conditions of the Chinese people.

    Therefore, effective measures should be taken as soon as possible to stop its happening. So how should we deal with the frightening sandstorms?

    Some experts offer practical advice as follows: For one thing, more money ought to be put into tree planting and forest protection in order to keep more water on the Earth. For another, government of all countries should make laws on environment protection. For example, banning the use of throw-away chopsticks and punishing illegal tree cutting. Scientists should also study and find ways to lower the grade of its destruction and to improve the environment. As for some schools, education about sandstorms should be spread properly and timely to make more and more people attach great importance to this problem.

    How people look forward to sunny days with soft wind touching their faces now and forever! The golden days can come back so long as we try our best to protect the natural environment from today on. And the fact is that what I expect is not just a dream. There are some sweet fruits from the early efforts.

    Very few people enjoy going to the dentist, especially for a filling. Often fillings need to be replaced during the patients' lifetime. But is filling the cavity (蛀洞)with a foreign material really the best treatment? What if the tooth could repair itself with its own material–dentine(齿质)? Researchers at King's College London have found a process that may replace the traditional method.

    Paul Sharpe of King's College says a new treatment for cavities is simpler. It uses a drug that causes the tooth to fill in the hole naturally with dentine. "It involves putting a drug in the hole. It excites a natural process, which starts to occur anyway following the damage, so you can actually get the big hole repaired and the repair is a production of the natural material, the dentine."

    Usually a new drug requires repeated testing before it is approved for treatment. However, this drug that produces the re-growth in teeth has already been approved. It is a drug used to treat Alzheimer's disease and other disorders of the nervous system. Researchers explain that they use only a small amount and they use it locally. Usually that means the medicine is put directly on the affected area. It does not travel through the patient's blood.

    Nigel Carter heads Britain's Oral Health Foundation. He describes the new treatment as an exciting possibility for dental care. But Carter also has a warning. "Actually re-growing the tooth that has been lost with a cavity would be really a huge step forward. But, it's also important that we remember that we shouldn't be getting the cavity in the first place. We're talking about a totally preventable disease."