实施价格歧视的前提有（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31439' and id < 2520431 and id<>'2520431' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31439' and id > 2520431 and id<>'2520431' order by id asc limit 5