I've gone over this a hundred times but for some reason I have a mental block against accepting the credited response (even though all the other choices are worse). Maybe one of you can hit upon the magic combination of words that will explain this in a way that I can understand...
June 2001 LSAT / Section 2 / Question 17
Dietary researcher: A recent study reports that laboratory animals that were fed reduced-calorie diets lived longer than laboratory animals whose caloric intake was not reduced. In response, some doctors are advocating reduced-calorie diets, in the belief that North Americans' life spans can thereby be extended. However, this conclusion is not supported. Laboratory animals tend to eat much more than animals in their natural habitats, which leads to their having a shorter life expectancy. Restricting their diets
merely brings their caloric intake back to natural, optimal levels and reinstates their normal life spans.
Which one of the following, if true, would most weaken the dietary researcher's argument?
(A) North Americans, on average, consume a higher number of calories than the optimal number of calories for a human diet.
(B) North Americans with high-fat, low-calorie diets generally have a shorter life expectancy than North Americans with low-fat, low-calorie diets.
(C) Not all scientific results that have important implications for human health are based on studies of laboratory animals.
(D) Some North Americans who follow reduced-calorie diets are long-lived.
(E) There is a strong correlation between diet and longevity in some species of animals.
Credited response: A
Just *how* does (A) weaken the dietary researcher's argument? It seems to strengthen the analogy between North Americans' dietary habits and laboratory animals' dietary habits, so if North Americans also consume a higher number of calories than the optimal number for a human diet just like laboratory animals eat much more than animals in their natural habitats, then this also leads to North Americans having a shorter life expectancy. Thus, putting North Americans on reduced-calorie diets will only bring their caloric intake back to natural optimal levels and merely reinstate their normal life spans instead of extending it. Isn't this basically what the dietary researcher is saying?