不易通过血脑屏障的物质是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31091' and id < 2501166 and id<>'2501166' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31091' and id > 2501166 and id<>'2501166' order by id asc limit 5