包装箱为何是packing case而不是packed case?

包装箱为何是packing case而不是packed case? Packing Packing packing packing packing 为何血糖不高而尿糖高 为何血糖不高而尿糖高 黄河为何是第2长河?黄河为何称为第2长河?而不称为第2大河? 为何返回舱能穿越大气层而不化,轨道舱却不行?是否是材质不一样? 项羽为何失去天下?是否是因为项羽在鸿门宴不杀刘邦而失去天下? 孟子称孔子是集大成者,为何孔子周游列国而不为重用,一生颠沛流离? 逗号的用法:While I was having dinner,my brother was packing.While I was having dinner,my brother was packing.是否可以：While I was having dinner my brother was packing.如 toddzhang123 老师的提议，这句话可以不使用逗号，而 为何液氨,液氯,金刚石不导电而氯水可导电?金刚是不是由C构成的嘛?为何液氨是纯净的而氨水是混合物?怎么区分? 当今时代 读书到底是为何?为何而读书? 生命到底是为何而存在的? 为何水煤气是不可再生能源 盐酸为何是混合物 Packing:export standard packing