家里的白炽灯用久了会发黑，这是因为（ ）。（常考）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='29942' and id < 2428048 and id<>'2428048' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='29942' and id > 2428048 and id<>'2428048' order by id asc limit 5