Comparative advantage refers to the ability of a party to produce a particular good or service at a lower opportunity cost than another. Even if one country has an absolute advantage in producing all goods, different countries could still have different comparative advantages
I believe the answer is option a
Answer to 1st question: They dug irrigation systems and canals to get the water to their crops.
Answer to 2nd question: They knew how to boost the immune system and they knew how to get the body to produce more white-blood cells. They also had a 90% success rate on surgeries, including brain surgeries.
Answer to 3rd: He had a big army and long roads leading all over his empire so if there was an uprising his army could travel quickly.
Hope this helps, have a good day. c;
This would be a perfect example of the system of barter as you are trading one book for the other. You can see from here what barter is, a trading system which involves direct exchange of goods without some kind of medium of exchange, for example money. Services can also be traded this way.
