________ her, she would have jumped into the river．A.If I had stoppedB.Unless I had stoppedC.If I hadn't stoppedD.If I didn't stop
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C解析一般情况下unless可与if…not互换，但在有些情况下二者是不能互换的，其中之一就是unless不能用来引导虚拟条件句，故不能选B．当所述情况与过去的事实相反时，虚拟条件句用过去完成式．又根据句意，从句应为否定含义，故同时排除A和D．