反义疑问句 it is hard to say ,下一句是什么

it is hard to say
ad. 难以断言(很难说)
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说明：否定前缀不能视为否定词，其反意疑问句仍用否定形式。
It is impossible, isn't it?
He is not unkind to his classmates, is he?
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故下一句应该是：
It is hard to say, isn't it?
很难断言，难道不是吗？