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Hi, dear MG Staff. I have qusetions on this problem. Why B is the best answer? I think that the construction "in their struggle" does not clearly state against which the opposition is, and therefore changes the meaning of orignal sentence. Besidies, whether the "did" in Choice B can be removed? It seems to me that the omission of "did" does not render any ambiguity of the comparison between "trade unions" and "Labour movements". In fact, i prefer Choice A to B.