单选题Theresearchissodesignedthatonc

单选题 The research is so designed that once ________ nothing can be doneto change it.A.beginsB.having begunC.beginningsD.begun

D解析对本题设空之前once一词用法的判断是做出正确选择的关键：once(或者其他连词如when，while，since等)引导状语从句时，如果从句主语与主句主语一致，可以省略其中的主语和be动词谓语结构，例如：Once in bed, the children usually stay there.(=Once they are in bed, the children usually stay there.)When finished, the building will be opened by the Prince of Wales.(=When it is finished, the building will be opened by the Princeof Wales.)While at college (=While she was at college), Delia wrote a novel.本题所给句子的句意为：The research is so designed that once it (=the research)is begunnothing can be done to change it．也就是：...once begun nothing can be done to change it．

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