Seeming to be the only organization fighting for the rights of poor people in the South,Hosea Hudson, a laborer in Alabama, joined the Communist party in 1931.
Choice A and B wrongly identify Hosea Hudson, not the communist party, as the organization under discussion. In choice C, the plural pronoun they does not agree in number with the singular noun party. In that in C and Since in D are less direct and idiomatic than Because in this context, and to be is needed to complete the predicate begun by seemed. E is the correct answer for this question of middle difficulty