LSAT-4-3-12. The number of North American children who are obese—that is, who have more body fat than do 85 percent of North American children their age—is steadily increasing, according to four major studies conducted over the past 15 years. If the finding reported above is correct, it can be properly concluded that (A) when four major studies all produce similar results, those studies must be accurate (B) North American children have been progressively less physically active over the past 15 years (C) the number of North American children who are not obese increased over the past 15 years (D) over the past 15 years, the number of North American children who are underweight has declined（C） (E) the incidence of obesity in North American children tends to increase as the children grow older 为什么选C呢？D怎么不对了？
