The answer to your question would be property.
Answer: Merchants from different places exchange one type of coin to another.
Explanation: Moneychangers were in (virtually) every city's harbor. Traders from foreigns country came to moneychangers to change their money to the local currency (AKA local coin) so that the traders could do buisness in that country
Answer:
The slaves would be sent with the person who bought them and would be taken to their master's plantation to be put to work.
I think the father of economics is Adam Smith
A, B, and C. Mesopotamia was in the middle of a desert, and the only reason it was farmable was because it lay between the Tigris and Euphrates rivers which flooded yearly to water the ground.