单选题 According to a 1980 survey, ten percent of all United States citizens over the age of sixteen are functionally illiterate. Therefore, if the projection that there will be 250 million United States citizens over sixteen in the year 2000 is correct, we project that 25 million of these citizens will be functionally illiterate.
Which of the following, if true, would most weaken the conclusion drawn by the author of the passage above?

A、 The percentage of high school graduates who do not go on to college has grown steadily over the past two decades.
B、 From 1975 to 1980 there was a three-percent decrease in the rate of functional illiteracy among United States citizens over the age of sixteen.
C、 Many United States citizens included in the 1980 survey would also be included in a survey conducted in the year 2000.
D、 Surveys that are improperly designed usually provide inaccurate results.
E、 (E) In 1980 sixty five percent of all United States citizens were over the age of sixteen.

【正确答案】 B

【答案解析】[解析] 本题是由一个survey而外推，其段落推理成立所隐含的假设是A与B的探讨对象之间无本质差异。就这个推理而言，其隐含假设是16岁的美国公民的文盲比例不变。因此反对应找变化点，而(B)刚好指出了这种变化，所以(B)为正确答案。