当塔顶放大器电源线室外部分长度为20m时，需做（）处接地。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='28907' and id < 2354688 and id<>'2354688' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='28907' and id > 2354688 and id<>'2354688' order by id asc limit 5