“Keep out or I'll chase you out! This is my property!” You hear this every spring. It is a long musical sound —a bird song! Birds use their songs to communicate different messages to one another. People who study bird sounds are learning their meanings.

    Usually it is the male that sings. Early in spring he sings to say that he has picked out a piece of property. He sings to attract a female of his same kind. Together they will raise a family in his territory (领地). He sings to tell all other birds of his kind to keep out.

    Each kind of bird has its own type of song. Cardinals sing something that sounds a little like “What cheer, cheer, cheer.” Towhees sing, “Drink your tea.”

    Most of the time, birds pay attention only to the songs of birds of their own kind. Cardinals answer cardinals, and song sparrows answer song sparrows. A cardinal knows that a song sparrow will not try to steal its mate. So you can see one reason why a cardinal may chase away another cardinal but will not bother a song sparrow.

    Most different kinds of birds eat different things. To find enough to eat, a bird needs a big piece of land to search in. Many kinds of birds have some ways of dividing up the land into territories. Song sparrows, cardinals ovenbirds, and white-throated sparrows are some of the birds that have territorial systems.

    Especially in early spring, birds work out the boundaries between their territories by singing “keep out” threats and by chasing and fighting each other. The birds continue singing to tell females that they have set up territories. Neighboring birds seem to agree that there are make believe fences between their pieces of property. Then they do not have to waste energy chasing each other instead of taking care of their young.

    Scientists guessed that some birds could recognize their neighbors by small differences in their songs. Two scientists who studied white-throated sparrows found that these birds can even tell the difference between songs of individual birds of their own kind. White-throated sparrows have songs that seem to say “I'm your neighbor” or “I'm a stranger” or “I'm your neighbor to the west.” Other kinds of birds could tell neighbors from strangers by their songs, too.

    If you think your vocabulary is weak, a little effort every day over six to nine months can go a long way in improving it. Here are some tips for increasing your vocabulary.

    {#blank#}1{#/blank#}. You may be comfortable reading a particular part of the newspaper but make an effort to read different articles on every page. The editorial (社论的) page is highly recommended not only for vocabulary but also for structuring and presenting thoughts.

    Make it a habit to read a new book every week. {#blank#}2{#/blank#}. You can consider becoming a member of the local library. Make a list of new words and look up their meanings in the dictionary.

    Watch English movies and television shows. It's an interesting way to enrich your vocabulary. {#blank#}3{#/blank#}.

    Use vocabulary cards. Vocabulary cards are used by students who are trying to learn many words in a short time. You can make your own cards by writing the word on one side and the meaning on the other side of a piece of paper. {#blank#}4{#/blank#}.

    Use the Internet. The Internet is an unlimited resource for reading material.

    {#blank#}5{#/blank#}. You will come across plenty of material to read. The Internet will also introduce you to new words. Be sure to look them up in a dictionary.

A. Read the newspaper every day.

B. Everyone has his own way of choosing books.

C. Vocabulary is important for you to learn English well.

D. Pick up a topic you like and search for articles about it.

E. Besides, by doing this you can learn the correct pronunciation as well.

F. Flash cards are a convenient tool to use to learn new words in your free time.

G. It is not surprising that those who read a lot of books develop good vocabulary.

    According to sociologists(社会学家), every modern industrial society has some form of social stratification(阶层). Class, power and status are important in deciding people's rank in society.

    Class means a person's economic position in society. A commonly used classification is lower class, middle class and upper class. While sociologists disagree on how these terms should be exactly defined, they do describe societies like the United States quite well. One study shows that 53% of Americans belong to the lower class, 46% the middle class, and 1% the upper class. Interestingly, a surgeon earning $500,000 a year and a bus driver earning $50,000 a year both regard themselves as the middle class!

    Power refers to the amount of control a person has over other people. Obviously, people in positions of great power (such as governors) exercise(行使)big power, but people who take orders from others have less power. Power and class do not always go hand in hand, however. For example, the governor of a state has great power, but he or she may not belong to a corresponding (相应的)economic class. Generally, however, there is a relationship between power and class. To our knowledge, there aren't too many people who aren't millionaires in the U．S. Senate!

    Status is the honor or respect attached to a person's position in society. It can also be affected by power and class, but not necessarily so. For example, a university professor may have a high status but not belong to a high social class or have a lot of power over others.

    Reports tell us that Americans work more and vacation less than people in other major industrial countries. Still, millions of Americans do try to get away from home for a week or two in the summer months. Some might even have the time and money to spend longer on vacation.

    For example, many retired Americans can be found driving around the United States in big recreational vehicles, known as R. V.'s. These serve as a home away from home. In fact, it might even be their only home as they see the country.

    Some American families get in their cars and drive to historic places like Colonial Williamsburg in Virginia. There, they can experience what life was like for early Americans. If that is not exciting enough, also in Williamsburg is a water park and an amusement park with rides.

    Other Americans visit national parks like Yellowstone or Yosemite out in the West. They want to spend time with nature. Or they take their vacation by a lake or the ocean. They might swim or fish. But many just want to sit and enjoy the feeling of doing nothing, except maybe read a book.

    Some families fly to other countries on vacation. Or they go on a cruise ship (大型游轮) and stop in different ports. Cruise ships are like floating cities.

    But not everyone goes someplace special on vacation. This might be the only time for people to work on things like home improvement projects. And while they do that, they might think of all the fun their friends are having.

    A few years ago, my wife, Sue had some serious health problems. She had suffered surgery after surgery and had also put on weight. Diets had not helped her and she suffered constantly from undiagnosed pain. One day the whole family sat down and drew up a “wish list”. To our surprise, one of Sue's items was to run in a marathon. Given her history and physical limitations, I thought her goal was completely unrealistic, but Sue became committed to it.

    She began by running very slowly and every day she ran just a little farther than she did the day before. Soon she could run three miles. Then five. Sue kept practicing and longed to run in the St. George Marathon in southern Utah.

    On the big day, I parked our van near the finish line, waiting for Sue. The rain was steady and the wind was cold. The marathon had started over five hours ago. The fast and strong competitors had finished already. Several cold and injured runners had been transported past me, and I began to panic. The image of Sue, alone and cold, off the road somewhere, made me sick with worry.

    Another hour passed and I spotted a small group running up. As they approached, I could see Sue, in the company of three others, and a woman in her twenties was near Sue. It was obvious that they had become friends during the race. I could see her begin to struggle. But when the finish line came into sight, she confidently even happily picked up her pace the last hundred yards to the finish line. Few people were left to congratulate my wife. They openly praised and embraced her, “She made us believe we could do it,” her new friend stated.

    From then on, she was carrying herself differently. Her head was more upright. Her shoulders were squared. Her walk had a new confidence. Her voice held a new, quiet dignity. It was not as if she had become someone new; it was more as if she had discovered a real self she had not known before. It was perseverance that made her realize she was an undiscovered masterpiece with a million things left to learn about herself. She truly liked her newly discovered self. So did I.

    Australia is a developed country and the future of its solar industry is looking bright after a record 3.5m panels (嵌板) were installed on rooftops last year, giving the equal output of a medium-sized coal-fired power station. The record 1,057 MW of capacity (生产能力) in small-scale systems installed across the country broke the previous record set in 2012, figures from the Clean Energy Regulator showed on Tuesday.

    Australia's solar power prosperity could almost double capacity in a year. The data also revealed that the average system size has also doubled since then from three to six kilowatts as average prices continued to fall. A fully installed 5KW system costs an average of $5,930 in Australia, according to the energy broker Solarchoice. net. au. Its records show that the price has roughly halved in many capital cities since 2012.

    The regulator's executive general manager, Mark Williamson, said there was increasing interest in renewals as a way to take control of electricity bills. But more importantly, he said it was also good news for reducing carbon emissions.

    “We are seeing a wide cross-section of Australians-households, community centers, schools, and small businesses-receiving rewards under the small-scale renewable energy scheme,” Williamson said. “Our data shows consumers are embracing renewable energy to take control of their electricity bills.”

    In 2017, there was a 41% increase in installing renewable energy capacity across all states and territories compared to 2016. Queensland led the way with installed capacity at 295MW, with the Australian Capital Territory taking top place for the biggest annual increase by 57%. “The data collected by the Clean Energy Regulator in 2017 reflects the industry is going from strength to strength. It looks like 2018 will be another big year for the solar industry.”

    The total of installed capacity for last year is expected to rise to 1,070MW when all the data is collected. A large coal-fired power station such as Loyd Yang A in Victoria's Latrobe Valley has a capacity of 2,200MW.