填空题 The average lifespan for these men 1 (should be) 68 years, if they'd aged twice as fast during their years in office as the popular wisdom suggests they do.
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【正确答案】 1、should have been    
【答案解析】[解析] 从句使用“had aged”结构表示对过去的虚拟，故主句应使用“should have been”结构表达对过去事实的假设。