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 You can not imagine the difficulty they had ____ the problem. It isn’t ____ easy.

A. to solve; so       B. solved; so        C. solving; that        D. solved; that

You can not imagine the difficulty they had ____ the problem. It isn’t ____ easy.

A. to solve; so       B. solved; so        C. solving; that        D. solved; that

You can not imagine the difficulty they had ____ the problem. It isn’t ____ easy.