National borders
(The Schengen agreement removes any controls at these between most EU neighbors)答案:国家边界 (National borders)点评:这道题是Ken抢答到的。沃森在第二的位置给出了边界的答案。
Sub-national boundaries
国家边界(state boundary)是确定国家领土范围的界限、划分一国领土与他国领土、一国领土与公海或专属经济区及一国领空与外层空间的界限。