单选题 The number of people 85 or older in the United States started increasing dramatically during the last ten years. The good health care that these people enjoyed in the United States during their vulnerable childhood years is primarily responsible for this trend.
Which of the following, if true, most seriously weakens the explanation above?

A、 Seventy-five percent of the people in the United States who are 85 or older are the children of people who themselves lived leas than 65 years.
B、 The people in the United States who are now 85 represent an age group that was smaller in numbers at birth than the immediately preceding and succeeding age groups.
C、 Thirty-five percent of the people in the United States who are 85 or older require some form of twenty-fourhour nursing care.
D、 Many of the people in the United States who are 85 or older immigrated to the United States when they were 20 years old or older.
E、 (E) Because of decreased federal funding for medical care for pregnant mothers and for children, the life expectancy of United States citizens is likely to decrease.

【正确答案】 D

【答案解析】[解析] 要反对本题的结论，就要反对结论所依赖的前提，本题的段落中把人们年龄的增加归结为人们在孩提时代受到了良好的健康医疗照顾。因此凡是能对人们在孩提时代受到了良好的健康医疗照顾构成反对的选项都是正确答案。(D)指出美国很多85岁以上的人是在20岁或20岁以后才移居美国的，也就是说这些人在孩提时代是不可能接受良好的健康医疗照顾的，因此(D)正确。(A)、(C)都与本题的结论无关；(B)引入了新的比较，所以(B)也是不对的。