| 41. | the four thousand miles frontier between the United States and Canada |
| 美国与加拿大之间长达4000英里的边界
|
| 42. | the Italian frontier of France |
| 法国毗连意大利一侧的边界
|
| 43. | sea frontier |
| (美）海疆防御指挥部
|
| 44. | on the Sino-Mongolian frontier |
| 在中蒙边界
|
| 45. | at the frontier of space exploration |
| 在太空控索的新领域
|
| 46. | a town [city] on the frontier |
| 边境城镇[市]
|
| 47. | forts on the frontier |
| 边境上的要塞
|
| 48. | the frontier between love and friendship |
| 爱情与友谊之间的界线
|