一个公比为2的等比数列，第n项与前n-1项和的差等于5，则此数列前4项之和为（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30930' and id < 2489317 and id<>'2489317' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30930' and id > 2489317 and id<>'2489317' order by id asc limit 5