Mary ________ the Washington Science Center for once. She is diasppointed that her father doesn't allow her to go there with her class.A.often es toB.was going toC.has never visitedD.had never been to
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C解析导解：从第二句可知，她从未去过，因此选C．句中for once表示“就这一次”，never…for once表示“一次都没有”．