（A） reveal some of the assumptions underlying their theory

　　（B） summarize a major finding of their experiments

　　（C） point out that their experiments were limited to the mouse

　　（D） indicate that their experiments resulted only in general correlations

　　（E） refute the objections made by supporters of the older theory

　　9. The last paragraph of the passage performs which of the following functions？

　　（A） Describes a disconfirming experimental result and reports the explanation given by

　　Snyder et al in an attempt to reconcile this result with their theory.

　　（B） Specifies the basis for the correlation observed by Snyder et al and presents an explanation in an attempt to make the correlation consistent with the operation of psychoactive drugs other than caffeine.

　　（C） Elaborates the description of the correlation observed by Snyder et al and suggests an additional explanation in an attempt to make the correlation consistent with the older theory.

　　（D） Reports inconsistent experimental data and describes the methods Snyder et al will use to reanalyze this data.

　　（E） Provides an example of the hypothesis proposed by Snyder et al and relates this example to caffeine's

　　properties.

　　Passage 4

　　Since the only 1970's， historians have begun to devote serious attention to the working class in the United State. Yet while we now have studies of working-class communties and culture， we know remarkably little of worklessness， When historians have focused on the Great Depression of the 1930's. The narrowness of this perspective ignores the pervasive recessions and joblessness of the previous decades， as Alexander Keyssar shows in his recent book. Examining the period 1870-1920， Keyssar concentrates on Massachusetts， where teh historical materials are particularly rich， and the findings applicable to other industrial areas.

　　（The unemployment rates that Keyssar calculates appear to be relatively modest， at least by Great Depression standards： during the worst years， in the 1870's and 1890's， unemployment was around 15 percent）。 Yet Keyssar rightly understands that a better way to measure the impact of unemployment is to calculate unemployment frequencies-measuring the percentage of workers who experience any unemployment in the course of a year. Given this perspective， joblessness looms much larger.

　　Keyssar also scrutinize unemployment patterns according to skill level， ethnicity， race， age， class， and gender. He finds that rates of joblessness differed primarily according to class： those in middle-class and white-collar occupations were far less likely to be unemployed. Yet the impart of unemployment on a specific class was not always the same. Even when dependent on the same trade， adjoining communities could have dramatically different unemployment rates. Keyssar uses these differential rates to help explain a phenomenon that has puzzled historians the startlingly high rate of geo-graphical mobility in the nineteenth-century United States. But mobility was not the dominant working-class strategy for coping with unemployment， nor was assistance from private charites or state agencies. Self-help and the help of kin got most workers through jobless spells.

　　While Kayssar might have spent more time developing the implications of his finding on joblessness for contemporary public policy， his study， in its thorough research and creative use of quantitative and qualitative evidence， is a model of historical analysis.