How time flies!Three years (_)

has passed
have passed
is past
are past

为什么

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has passed (表示时间、距离、重量、金钱等作主语把它枣晌看作一个整凳行锋体，谓语动词用单数，带竖排除HAVE PASSED， ARE PAST ，而PAST 是介词，再加上时间过去，不用被动语态）

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have passed

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