听力题 Half a century ago, most American children grew up in the home of their two biological parents. Now, more than half will live apart from at least one parent before reaching the age of 18, and more than half of these will live with a step-parent or a foster parent. Disturbingly, three new studies, by Anne Case, an economist at Princeton university, and her colleagues, suggest that these children will do worse in terms of food, education and health care than other youngsters. One of these studies, published in the October issue of the Economic Journal, finds that households in the United States where a child is raised by a non-biological mother spend less on food than those where the relationship is biological. Whether the child is raised by a step-, adoptive or foster mother, the reduction is the same. Evidence from South Africa tells a similar tale: where a child does not live with its birth-mother, the household spends less on mild, fruit and vegetables, and more on alcohol and tobacco. Dr. Case''s other two studies find that children not raised by their birth-mothers suffer in other ways. One discovered that 61% of children over a year old and living with both biological parents had had a medical check-up in the past year; but only 46% of those living with a step-mother had had one. The other looked at education: A mother''s own children receive, on average, one more year of schooling than do step-, foster or adopted children.