Scientist think this region may have once been a large sea plains

How does specialization enable countries to trade with one another? a country can make and sell goods affordably and buy goods that it is inefficient at making. a country can make what it chooses and sell its goods to other countries. a country can decide to buy everything it needs from other countries. a country can efficiently make goods that were once difficult to make.

The biggest component / ingredient of summer time smog is

Any study/memorization tips? i have exams in a week and it would be great to try suggestions!you ; )