To get an extra 14 years of life, don't smoke, eat lots of fruits and vegetables, exercise regularly and drink alcohol in a proper amount.That is according to a study published this Monday in the Public Library of Science Medicine Journal. After tracking more than 20,000 people aged 45 to 79 years in the United Kingdom from about 1993 to 2007, Kay-Tee Khaw of the University of Cambridge and his colleagues found that people who adopted these four healthy habits lived all average of 14 years longer than those who didn't. "We've known for a long time that these behaviors are good things to do, but we've not seen this benefit before, "said Susan Jebb, head of Nutrition and Health at Britain's Medical Research Council."The benefit was also seen regardless of whether or not people were fat and what social class they came from." Study participants scored a point each for not smoking, regular physical activity, eating five servings of fruits and vegetables a day and moderate alcohol intake. Public health experts said they hoped the study would inspire governments to introduce policies helping people to adopt these changes.But because the study only observed people rather than testing specific changes, it would be impossible to conclude that people who suddenly adopted these healthy behaviors would surely gain 14 years. "We can't say that any person could gain 14 years by doing these things, "said Dr.Tim Armstrong, a physical activity expert at the World Health Organization."The 14 years is an average across the population of what's theoretically possible." "Most people know that things like a good diet matter and that smoking isn't good for them, "Susan Jebb said."We need to work on providing people with much more practical support to help them change." We can learn from the passage that  _  .
Susan Jebb did not take part in the study. the study observed people as well as tested specific changes. there's no need for people under 45 to adopt these good habits. only those from first class can benefit from these healthy behaviors.