正常后前位X线胸部平片，右心缘可见上下两个弓，上段弓由哪些器官组成：

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SQL Error: select id,body,options from ***_enewstiku where sourceid='24720' and id < 2117491 and id<>'2117491' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='24720' and id > 2117491 and id<>'2117491' order by id asc limit 5