Unit and measurement
One g is the force per unit mass due to gravity at the Earth's surface and is the standard gravity (symbol: gn), defined as 9.80665 metres per second squared, or equivalently 9.80665 newtons of force per kilogram of mass.
River valley trade made them key economic areas.
Hope this helped. :)
It is called Globalization
I'd have to say gas because it usually doesn't change at all
One way would be to limit who can receive a passport or visa to travel to another country and another would be at the entrance to the country they may not be admitted for example due to inadequate funds to live. In my case, when I travelled by bus from Costa Rica to Panama, the Panamanian authorities required that I either have a ticket out of the country or a return ticket back to San Jose, Costa Rica.
