During Roosevelt’s years in office Black Americans began voting for Democrats rather than Republicans in national elections, but Black support for Democrats（主语） at the state and local levels（介词短语） developed（谓语） only after Harry Truman’s support of civil rights legislation。（时间状语）
black是形容词。Black support for Democrats 的意思是黑人对于民主党的支持。
正确答案里没有and developed 呀？何谈平行呢？
Black support for Democrats 是与 Harry Truman’s support of civil rights legislation平行的。而且平行的很好。 | 
