Some of the most prosperous nations in the world have experienced a pronounced drop in national savings rates -- the percentage of after-tax income an average household saves. This trend will undoubtedly continue if the average age of these nations' populations continues to rise, since older people have fewer reasons to save than do younger people. Which one of the following indicates an error in the reasoning leading to the prediction above? ['It only takes into account the comparative number of reasons older and younger people, respectively, have for saving, and not the comparative strength of those reasons.', 'It fails to cite statistics showing that the average age of the population of certain nations is rising.', 'It uses after-tax income as the base for computing the national savings rate without establishing by argument that after-tax income is a more appropriate base than before-tax income.', "It assumes that a negative savings rate -- the result of the average household's spending all of its after-tax income as well as some of its existing savings -- cannot ever come about in any nation."]