The impact of Thoreau's “On the Duty of Civil Disobedience” might not have been so far-reaching ____ for Elizabeth Peabody, who dared to publish the controversial essay. A. if not having been B. it is not being C. had it not been D. is it not being(TOEFL) 这道题把我弄糊涂了，似乎 A、B、C、D 中没有一项是可选择的。
英语里有一种所谓的无连词条件从句。在这种从句里，不用表示条件的连词，而用主谓部分倒装的方法来标明非真实的条件关系。但并不是所有的动词或助动词都能用主谓部分倒装的方法来标明这种条件关系。实际上，只有少数几个助动词才具有这种功能：had, were, should, could, might。应记住，这种句型主要用于庄重的语体（尤其科技英语和法律英语）中：
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Were I you, I would study hard. (IME) 要是我是你的话,我就努力学习。
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Had I known, I would have written before. (CGEL) 要是我知道的话,我以前就写了。
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Should she be interested, I'll phone her. 如果她感兴趣的话,我就给她打电话。
请注意:在否定的条件句中,如果 had, were, should, could, might 放在句首,不能用-n't 这种缩略形式。
还应注意,这种无连词条件从句不仅可以放在主句之前,亦可放在主句之后:
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He could persuade her to make room for Miss Thornton should this be necessary. (Cronin) 如果必要的话,他会说服她给桑顿小姐让位的。
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John would have caught the bus had he hurried. (IME) 要是当时约翰赶紧走的话,他就赶上那辆公共汽车了。 (参见 had he been, were )