A Good Example of Open, Undemarcated Boundaries Would Be

Multiple Choice

A good example of open, undemarcated boundaries would be

A) between Switzerland and Germany where Switzerland is a Schengen member, but not an EU member.
B) between Pakistan and Afghanistan where there is little Pakistani government control of the border.
C) between Saudi Arabia and Yemen where no boundary has ever been drawn.
D) between the islands of Crete and Cyprus where boundaries cannot be drawn because of water.