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Ensuring an adequate water supply have been a concern ever since people began to live in t

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Ensuring an adequate water supply have been a concern ever since people began to live in towns and cities.

此题为多项选择题。请帮忙给出正确答案和分析，谢谢！

热搜：n维列向量组a1,an-1线性无关,且与非零向量正交

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  • 正确答案：have—has
    考查主谓一致。主语为动名词短语时，谓语动词应为单数形式，have应改为has。