which statements describe the decline of sumer?
choose all answers that are correct.
a. the swamps bred insects that carried disease.
b. the needed canals became too costly to build.
c. there was a lack of natural barriers that could discourage attack.
d. as the fields of sumer grew saltier, harvests became smaller.

Two gymnastics teams are intense rivals. the first team has started recruiting new gymnasts from different cities and even foreign countires in an effort to build a stronger team. after learning this, the secondteam begins its own recruitment campaign to find better gymnasts. over a period of months, each team recruits dozens of players, each time trying to find a better recruit than its rivals most recent addition. which idea from the cold war is most similar to this scenario