求翻译：由已婚夫妇及不满18岁孩子组成的核心家庭占全美家庭数的比例，从1990年的25.6％下降至2000年的23.5％，此数字较40年前更减少了45％。而由夫妇组成的家庭占全部家庭数比例也相应由55％降到52％。在同一时期，单身者家庭数上升至总数的26％；由非婚同居者组成的家庭数增长72％是什么意思？

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And does not reach the nuclear family by married couples which 18 year old child is composed to occupy the entire American family number the proportion, from 1990 25.6% drops to 2000 23.5%, this digital 40 years ago reduced 45%.But the family which is composed by husbands and wives accounts for the

Is made up of a married couple and children under 18 years old ratio of the number of nuclear families accounted for families throughout the United States, declined from per cent in 1990 to per cent in 2000, this figure more 45% less than the 40 years ago. Proportion of total family number of the fa

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