关于OG11th-89的翻释问题

Passage 16

In 1955
                Maurice Duverger published The

Political Role of Women, the first behavioralist,

multinational comparison of women’s electoral

participation ever to use election data and survey

(5)data together.
                His study analyzed women’s patterns

of voting, political candidacy, and political activism

in four European countries during the first half of

the twentieth century. Duverger’s research findings

were that women voted somewhat less frequently

(10)than men
            (the difference narrowing the longer

women had the vote) and were slightly more
                

conservative.

      推导题（E）

        the difference narrowing the longer

women had the vote

(A)   Were most politically active

(B)    Ran for office most often

(C)   Held the most conservative political views

(D)   Had the most egalitarian relations with men

(E)    Had possessed the right to vote for the shorted time

关于这题，我知道是在考这句话，但是我不懂"the difference narrowing the longer women had the vote"的意思，我的想法是一个插入的主词"the difference which is narrowing(差距正在缩减中)"，但是后面的"the longer women had the vote"不知道怎么做解释？？

请ｎｎ指点！！

谢谢