The equalibrium price is the perfect point of which a good or services prices. That is why there is no room for excess demand or supply .
The difference between tribes can be literally anything from where they originate in the U.S. their economic systems, social hierarchy, the types of buildings used, their way of life [such as hunter-gatherer or agrarian], to their belief system. In conclusion it is reasonable to conclude that the differences are far greater than similarities
The answer should be D.
They were found in Islam