某微机保护的采样频率为4kHz，则信号调理部分抗混叠滤波器的截止频率至少为(    )。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69532' and id < 4505203 and id<>'4505203' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69532' and id > 4505203 and id<>'4505203' order by id asc limit 5