Which of the following systems of trade was most widely used in both ancient river civilizations and ancient Native American civilizations? (4 points) a
bartering

b
the exchange of coined money

c
free exchange

d
international trade

Bartering

Explanation:

Bartering system of trade was most widely used in both ancient river Civilization and ancient native American civilization due to the following reasons: - Services and goods are traded in bartering with another person where there is no money involved.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.