当发生区内故障且高频发信机故障无法发出信号时，可以正确动作的发信类型是（   ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id < 4491470 and id<>'4491470' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id > 4491470 and id<>'4491470' order by id asc limit 5