By now you should have noticed that trade becomes important to people as they settle down and develop more complex societies. What advantages does a society gain when it engages in trade?

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

the dominoes began to fall. the surrender at appomattox took place a week later on april 9. while it was the most significant surrender to take place during the civil war, gen. robert e. lee, the confederacy's most respected commander, surrendered only his army of northern virginia to union gen. ulysses s. grant

explanation:

it should be a. song dynasty’s civil service examination system created an administrative bureaucracy manned by the landed aristocracy.

people had jobs and began to work. that’s why the commercial revolution was great.