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蓝皮P168-9

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.

A)      Seeming to be

B)    As

C)     In that they seemed

D)     Since it seemed

E)      Because it seemed to be

我选的是B，答案给的E，用because，这句话没有主句吗？我的理解

Because it seemed 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. 黄的全部是修饰，然后because是一句条件状语从句，那主句呢？