America is a mobile society. Friendships between Americans can be close and real, yet disappear soon if situations change. Neither side feels hurt by this. Both may exchange Christmas greetings for a year or two, perhaps a few letters for a while — then no more. If the same two people meet again by chance, even years later, they pick up the friendship. This can be quite difficult for us Chinese to understand, because friendships between us flower more slowly but then may become lifelong feelings, extending (延伸) sometimes deeply into both families.

    Americans are ready to receive us foreigners at their homes, share their holidays, and their home life. They will enjoy welcoming us and be pleased if we accept their hospitality (好客) easily.

    Another difficult point for us Chinese to understand Americans is that although they include us warmly in their personal everyday lives, they don't show their politeness to us if it requires a great deal of time. This is usually the opposite of the practice in our country where we may be generous with our time. Sometimes, we, as hosts, will appear at airports even in the middle of the night to meet a friend. We may take days off to act as guides to our foreign friends. The Americans, however, express their welcome usually at homes, but truly can not manage the time to do a great deal with a visitor outside their daily routine. They will probably expect us to get ourselves from the airport to our own hotel by bus. And they expect that we will phone them from there. Once we arrive at their homes, the welcome will be full, warm and real. We will find ourselves treated hospitably.

    For the Americans, it is often considered more friendly to invite a friend to their homes than to go to restaurants, except for purely business matters. So accept their hospitality at home!

    Social media is one of the fastest growing industries in today's world. A study conducted by the US Pew Research Center showed that 92 percent of teenagers go online daily. The wide spread of social media has changed nearly all parts of teenagers' lives.

    Changing relationships

    High school student Elly Cooper from Illinois said social media often reduces face- to-face communication. “It makes in-person relationships harder because of people's attention given to their phones instead of their boyfriends or girlfriends,” Cooper said.

    Yet, some people believe social media has made it easier to start relationships with anyone from anywhere. Beth Kaplan from Illinois met her long-distance friend through social media. He currently lives in Scotland, but they're still able to frequently communicate with each other. “I can feel close to someone that I'm talking to via FaceTime,” Kaplan said.

    Wanting to be “liked”

    The rise of social media has changed the way teenagers see themselves. The 19- year-old Essena O'Neill announced on the social networking service Instagram that she was quitting social media because it made her unable to stop thinking about appearing perfect online. Negative comments also can do great damage to a teenager's self-esteem. Teenagers who get negative comments can't help but feel hurt.

    Opening new doors

    However, Armin Korsos, a student from Illinois, takes advantage of the comments he receives over social media to improve his videos on the social networking site YouTube. “Social media can help people show themselves and their talents to the world in a way that has never been possible before,” Korsos said.

    Car companies are developing vehicles that will plug into electric sockets(电源插座), just like many laptops, digital cameras, cell phones and MP4 do. Called "plug-in vehicles", these cars will get most of their power from electricity. Their drivers won't have to stop at gas stations as often as usual.

    The technology is more than just cool. In our car-filled world, plug-in vehicles could reduce the amount of gas we use, which keeps rising in cost now and then. Besides, driving around in these vehicles may even help the environment. Gas-burning cars produce a lot of greenhouse gas, which causes global warming.

    The first company-produced plug-in vehicles could hit the roads by 2020. But engineers still have a lot of work to do to make the technology practical and inexpensive.

    Batteries are the biggest challenge. In the plug-in-vehicle world, Li-ion(锂离子)batteries are getting the most attention. These batteries can store a large amount of energy in a small package, and they last a longer time between charges. Li-ion batteries can fit laptops, cell phones, heart instruments and other similar pocket ones.

    But because cars are so big and heavy, it would still require a suitcase-sized Li-ion batteries to power about 12km of driving. What's more, the batteries are much expensive.

    "A car filled with batteries could go a long distance," says Ted Bohn, an electrical engineer in Chicago. "But it couldn't pull any people, and it would cost $100,000." So researchers need to work out how to make batteries smaller and cheaper, among other questions.

    "The answers don't exist yet." Bohn says, "As a kid, I thought someone someplace knows the answer to everything. All of these questions haven't been decided. But that's what engineering is about--making a guess, running tests and getting fine results."

    If you want to be a volunteer, you have to answer the following typical questions. Do you want to work with people, animals or machines? Do you want to work indoors or outdoors, directly serve people in need or serve people behind the scenes? Every year, thousands of people in the west offer volunteer service. Volunteering greatly strengthens the community because it helps the old, the young, the weak, the sick, and the disabled and the injured to solve problems.

    Volunteers usually help in many different ways. They may give people advice, offer friendship to the young, drive the elderly to church (if up to the driving age), advise kids against drugs, work as assistants in schools or nursing homes, raise funds, plant trees, help out in local libraries and do many other things. Volunteering can be a few hours a week or a few hours a month. Anybody who wants to serve people in need can become a volunteer.

    In fact, the art of volunteering is a process of both giving and receiving. Volunteering allows volunteers to meet new people, make new friends and mix with people from all walks of life. Volunteering is an excellent way to experiment and try out new techniques and skills, discover your individual talents and explore career choice. Being a volunteer will take you on a wonderful journey and help you learn more than what you can get from books.

    At the age of 14, James Harrison had a major chest operation and he required 13 units (3.4 gallons) of blood afterwards. The blood donations saved his life, and he decided that once he turned 18, he would begin donating blood as regularly as he could.

    More than 60 years and almost 1,200 donations later, Harrison, whose blood contains an antibody(抗体) that has saved the lives of 2.4 million babies from miscarriages (流产), retired as a blood donor on May 11. Harrison's blood is valuable because he naturally produces Rh-negative blood, which contains Rh-positive antibodies. His blood has been used to create anti-D in Australia since 1967.

    "Every bottle of anti-D ever made in Australia has James in it," Robyn Barlow, the Rh program director told the Sydney Morning Herald. "It's an amazing thing. He has saved millions of babies. I cry just thinking about it." Since then, Harrison has donated between 500 and 800 milliliters of blood almost every week. He's made 1,162 donations from his right arm and 10 from his left.

    "I'd keep going if they let me," Harrison told the Herald. His doctors said it was time to stop the donations — and they certainly don't take them lightly. They had already extended the age limit for blood donations for him, and they're cutting him off now to protect his health. He made his final donation surrounded by some of the mothers and babies who his blood helped save.

    Harrison's retirement is a blow to the Rh treatment program in Australia. Only 160 donors support the program, and finding new donors has proven to be difficult. But Harrison's retirement from giving blood doesn't mean he's completely out of the game. Scientists are collecting and cataloging his DNA to create a library of antibodies and white blood cells that could be the future of the anti-D program in Australia.

    Before you make friends, you have to decide who you want to be your friends.

    Most people like to have friends who like to do the same kind of things they do.

    The quickest way to make a friend is to smile. When you smile, people think you are friendly and easy to talk to. It may not be easy at first to smile, but remember most people will stay away from a scaled or angry looking.

    One easy way to start a conversation with someone is to say something nice about him. Think about how great you feel when someone says something nice to you. Doesn't it make you want to keep talking to that person?

    Ask your new friends questions about themselves. Who's their favourite singer, where do they live, what do they do after school are all good questions to start a conversation. Make sure you have something to add to the conversation, too. Then someone asks you a question, do have an answer for it. There is nothing that will stop a conversation quicker than a shrug for an answer.

    Kids who show an interest in other kids and who are kind and friendly make good friends. Remember, everyone wants to be around people who like to do similar things and people who are nice to them.