A-A+
Ensuring an adequate water supply have been a
问题详情
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！
参考答案
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。
考点：
