What makes Europe’s megalopolis challenge unique?

Here is a picture  of the net. its 4 squares in a row diagonal and on the third draw one square aove and under

Europe needs to build a trump-like wall that will spread across europe making it impossible for migrants to cross they need to spread pig guts all over this wall so the muslims will never consider crossing into europe..you might be asking "can't they just fly over with planes? " well yes they can so we will install thaad missile protections system to shoot down any aircraft that violates europe's air fourth would be to start a fourth reich in germany.. last but not least.. make europe great again!

The correct answer is a)  a resource with a limited supply; it will run out.