Exchange makes it possible for trading partners to produce more goods through division of labor and adoption of mass production methods. Both a and b are true. Middlemen add to the expenses of buyers without providing a benefit to sellers. Our economy would work just as well without middlemen since they do not expand the availability of physical goods. Middlemen reduce the number of transactions since they increase the buyer's price and reduce the seller's net receipts.
Middlemen create value by arranging trades and providing information to buyers and sellers.
All of the above are correct. A private owner of a resource has a strong incentive to conserve the resource for the future, particularly if it is expected to increase in value. According to the law of comparative advantage, a nation, individual, or region should trade for those economic goods for which it has an absolute advantage. Three basic decisions must be made by all economies. Attainable, but resources are used inefficient.