高频保护载波频率过低，如低于50KHz,其缺点是（   ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id < 4491463 and id<>'4491463' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id > 4491463 and id<>'4491463' order by id asc limit 5