单选题 .  ①Some historians have recently challenged the "party period paradigm," the view, advanced by McCormick and others, that political parties—especially the two major parties—in the United States between the years 1835 and 1900 evoked extraordinary loyalty from voters and dominated political life. ②Voss-Hubbard cites the frequency of third-party eruptions during the period as evidence of popular antipathy to the two-party regime. ③He correctly credits third parties with helping generate the nineteenth century's historically high rates of voter turnout by forcing major parties to bolster supporters' allegiance, lest minor parties siphon off their votes, and with pushing policy demands that the major parties ignored. ④Formisano stresses the pervasive record of nonpartisan and anti-party governance at the local level, and women's frequent participation in nineteenth-century public life, prior to their enfranchisement, in nonpartisan and antiparty ways as evidence of the limitations of the party period paradigm. ⑤Yet McCormick would deny that the existence of antiparty sentiment during the period undermined the paradigm, since he has always acknowledged the residual strength of such sentiment during the nineteenth century. ⑥In any case, the strength of the paradigm is its comparative thrust: the contrast it draws between the period in question and earlier and later political eras.24.  The primary purpose of the passage is to ______