Were it not for their support and help, we ______ able to finish the task ahead of time.A. were notB. should not have beenC. are notD. would not be

本题考查虚拟语气的用法，核心在于判断条件句的时态与主句的对应关系。

• 关键知识点：当条件句表示与现在事实相反的情况时，虚拟语气的结构为：
  If + 主语 + were/was..., 主句用 would + 动词原形。
• 破题关键：题目中条件句使用了 Were it not for...（省略了 if 的虚拟条件句），主句需用 would 表示对未来的虚拟，且 be able to 的否定形式为 would not be able to。

选项分析

• A. were not：表示过去时的虚拟，与题干中“提前完成任务”（未来动作）矛盾。
• B. should not have been：表示“本不该”，强调对过去的批评，不符合题意。
• C. are not：虚拟语气中主句不用现在时，且无法体现“未来”的虚拟性。
• D. would not be：正确体现与现在事实相反的虚拟语气，表示“将不能完成任务”。