Like a membrane, the border patrol controls what/who can enter a country or city. Border patrol can intercept certain substances such as drugs and send them back, or let them enter, as well as with people.
BARRIER, CONTROLS ENTRY AND EXIT OF MATERIALS/LIKE BORDER PATROL
Like a membrane, the border patrol controls what/who can enter a country or city. Border patrol can intercept certain substances such as drugs and send them back, or let them enter, as well as with people.