Which is not required for the development of civilization

In general, "a. cities" are not required for the development of civilization, since many civilizations throughout history have been comprised of smaller villages that would not compare to modern or pre-modern cities.  

he risk-return relationship. generally, the higher the potential return of an investment, the higher the risk. there is no guarantee that you will actually get a higher return by accepting more risk. diversification enables you to reduce the risk of your portfolio without sacrificing potential returns.

explanation:

d) a week

because the land run of 1889, although not without precedent in the history of the west, further, their men were aboard the first trains, ready to jump off and begin staking their claims. oklahoma city, edmond, and guthrie were all so affected.