border; frontier 短语和例子 封锁边境 close the frontiers; seal off the borders; 开放边境 open the borders or frontiers; 边境安宁 security of the border; 边境冲突 border clash; clash conflict; 边境地区 backcountry; border; 边境兑换 exchange of the frontier; 边境检查站 border check point; frontier inspection station; 边境交货 delivered at the frontier; 边境居民出入境通行证 boundary resident's entry [exit] certificate; 边境贸易 frontier trade; border trade; 边境市镇 border town; 边境事件 border incidents