问题描述：
both you and he are careful否定句
they have been to Nanjing twice对划线部分提问（划线的是twice）
____ _____ ____ have they been to Nanjing
they have been to Nanjing twice对划线部分提问（划线的是twice）
____ _____ ____ have they been to Nanjing
问题解答：
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