Abby Subark is a mother of two from Boston. "For my kids, I'm nervous. I don't know if they'll be able to achieve their American dream." She may be right. More than hard work or education, the best way to get rich in America is to be born rich. It is the case that somebody who is in the upper third of income, poor scores, in the bottom on tests when they are in eighth grade, is more likely to go to college and finish college than a poor kid with the top scores. That's what the working persons'  children are up against. The Economic Policy Institute finds it would take a poor couple with 2 children 9 or 10 generations to achieve middle class status. That's about 200 years. The hallmark   of American opportunity has always been the ability to do better than your parents. But compared with similar developed countries, the United States ranks fifth out of six for so-called intergenerational mobility  . If you look at the mechanisms   for upward mobility that were so readily available 50 years ago, they are becoming out of reach, like plentiful factory jobs with good wages and affordable education and health care. White families are twice as likely as blacks to be upwardly mobile. For most people in America today, _  If you started in the middle-income class, about 40 to 45 percent of what you are making right now is due to the fact that your parents were in the middle-income class. The rest is up to you. But for the millions of people who find themselves below the poverty line and the millions more who are the working poor, their starting point for the American dream leaves them painfully far away from the middle class. The main idea of the passage is   _  .
How the middle class comes about in the U.S. It's hard to realize the American dream for the poor. Wealth and social status depend on family background. Upward mobility in America is never easy.