What are the measures that countries take to prevent the entry of illegal migrants into their States?

When air at the surface diverges, airflow above must diverge, regardless of hemisphere converge in the northern hemisphere but diverge in the southern diverge in the southern hemisphere but converge in the northern converge, regardless of hemisphere?

What is a compass? how does it work

Which example gives the relative location of a place? 50 main street 33 degrees n latitude, 91degrees w longitude east of the library 1600 pennsylvania ave., washington, d.c.