Increase in a nations real GDP

the first successful, urban blues recording, selling more than 75,000 copies, was made in year 1920.

mamie smith recorded the first commercially successful example of the urban blues,   with the recording of “crazy blues”."crazy blues" was recorded on august 10, 1920, in new york city. within a month of the release of “crazy blues” it had sold 75,000 copies.

the answer is: objects or persons that are meaningful to you personally

for example, let's say that you are trying to study an outline about a historical event that happen on the middle ages. one thing you can do to make this easier to memorize is by replacing the people that involved in the event with the people that you know in your personal life. this would make you able to recall the information better.