这些山脉标志着两国之间的边界。

The mountains mark the ___boundary between the two countries.

在当今互联的世界里，地方性问题和全球性问题之间的界限常常很模糊。

In today's interconnected world, the ___boundary between local and global issues is often blurred.

一道栅栏标出了房屋后部的产权界限。

A fence marks the property ___boundary at the back of the house.