预付款担保的主要作用是（）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='24806' and id < 2121173 and id<>'2121173' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='24806' and id > 2121173 and id<>'2121173' order by id asc limit 5