As cultural symbols go， the American car is quite young． The Model T Ford was built at the Piquette Plant in Michigan a century ago， with the first rolling off the assembly line （装配线）on September 27， 1908． Only eleven cars were produced the next month． But eventually Henry Ford would build fifteen million of them．

    Modern America was born on the road，behind a wheel． The car shaped some of the most lasting aspects of American culture： the roadside diner， the billboard， the motel，even the hamburger． For most of the last century， the car represented what it meant to be American﹣going forward at high speed to find new worlds． The road novel， the road movie， these are the most typical American ideas， born of abundant petrol， cheap cars and a never﹣ending interstate highway system， the largest public works project in history．

    In 1928 Herbert Hoover imagined an America with "a chicken in every pot and a car in every garage．" Since then， this society has moved onward， never looking back， as the car transformed America from a farm﹣based society into an industrial power．

    The cars that drove the American Dream have helped to create a global ecological disaster． In America the demand for oil has grown by 22 percent since 1990．

    The problems of excessive（过度的） energy consumption， climate change and population growth have been described in a book by the American writer Thomas L． Friedman． He fears the worst， but hopes for the best．

    Friedman points out that the green economy（经济）is a chance to keep American strength． "The ability to design， build and export green technologies for producing clean water， clean air and healthy and abundant food is going to be the curreney of power in the new century．"

Children as young as ten are becoming dependent on social media for their sense of self﹣worth，a major study warned．

    It found many youngsters（少年）now measure their status by how much public approval they get online， often through "like"． Some change their behavior in real life to improve their image on the web．

    The report into youngsters aged from 8 to 12 was carried out by Children's Commissioner （专员）Anne Longfield． She said social media firms were exposing children to major emotional risks，with some youngsters starting secondary school ill﹣equipped to cope with the tremendous pressure they faced online．

    Some social apps were popular among the children even though they supposedly require users to be at least 13．The youngsters admitted planning trips around potential photo﹣opportunities and then messaging friends﹣and friends of friends﹣to demand "likes" for their online posts．

    The report found that youngsters felt their friendships could be at risk if they did not respond to social media posts quickly， and around the clock．

    Children aged 8 to 10 were "starting to feel happy" when others liked their posts． However，those in the 10 to 12 age group were "concerned with how many people like their posts"， suggesting a "need" for social recognition that gets stronger the older they become．

    Miss Longfield warned that a generation of children risked growing up "worried about their appearance and image as a result of the unrealistic lifestyles they follow on platforms， and increasingly anxious about switching off due to the constant demands of social media"．

    She said： "Children are using social media with family and friends and to play games when they are in primary school． But what starts as fun usage of apps turns into tremendous pressure in real social media interaction at secondary school．"

    As their world expanded． she said，children compared themselves to others online in a way that was "hugely damaging in terms of their self﹣identity， in terms of their confidence， but also in terms of their ability to develop themselves"．

    Miss Longfield added： "Then there is this push to connect﹣if you go offline， will you miss something， will you miss out， will you show that you don't care about those people you are following，all of those come together in a huge way at once．"

    "For children it is very， very difficult to cope with emotionally．" The Children's Commissioner for England's study﹣Life in Likes﹣found that children as young as 8 were using social media platforms largely for play．

    However， the research﹣involving eight groups of 32 children aged 8 to 12﹣suggested that as they headed toward their teens， they became increasingly anxious online．

    By the time they started secondary school﹣at age 11﹣children were already far more aware of their image online and felt under huge pressure to ensure their posts were popular， the report found．

    However， they still did not know how to cope with mean﹣spirited jokes， or the sense of incompetence they might feel if they compared themselves to celebrities（名人）or more brilliant friends online． The report said they also faced pressure to respond to messages at all hours of the day﹣especially at secondary school when more youngsters have mobile phones．

    The Children's Commissioner said schools and parents must now do more to prepare children for the emotional minefield（雷区）they faced online． And she said social media companies must also "take more responsibility"． They should either monitor their websites better so that children do not sign up too early，  or they should adjust their websites to the needs of younger users．

    Javed Khan， of children's charity Bamardo's， said： "It's vital that new compulsory age﹣appropriate relationship and sex education lessons in England should help equip children to deal with the growing demands of social media．

    "It's also hugely important for parents to know which apps their children are using．"