声波在进人不同介质时发生角度改变，该 改变的角度称为

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31793' and id < 2541706 and id<>'2541706' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31793' and id > 2541706 and id<>'2541706' order by id asc limit 5