The red line is the demarcation line.

红线就是国界线。

There is no demarcation line along the Yalu River.

鸭绿江是没有界线的。

Where is the demarcation line between Love and Friendship?

哪里是友情和爱情的细微分别？

But I think there should be a demarcation line to be observed.

但是，我认为，也必须有一个界限。

Curzon line: Demarcation line between Poland and Soviet Russia.

寇松线：波兰和苏俄之间的边界线。