[求助]

        In the United States, trade unions encountered far more intense opposition against their struggle for social legitimacy than the organized labor movements of most other democratic nations.

(A) against their struggle for social legitimacy than

(B) in their struggle for social legitimacy than did

(C) against their struggle for social legitimacy as

(D) in their struggle for social legitimacy as did（B）

(E) when they struggled for social legitimacy than has

please explain the reason?

根据比较形式，选择than而不是as。

补出谓语，说明比较的对象是主语。