Not until you try to build a machine that does the same task as people do ________．A.you realize how is it incredibly hardB.do you realize how incredibly hard it isC.you realize how incredibly hard is itD.do you realize how it is incredibly hard
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B解析not…until…“直到……才……”。not until如果放在句首，句子结构要倒装。在宾语从句中how修饰incredibly hard，故