Which conclusion is best supported by the information on the time line?

Assuming that this is referring to the same timeline image that was posted before with this question, the correct response would be that the development of agriculture led to increases in productivity and civilizations, since the major civilizations of the world all come after this time period. 

They made a checks and balance system to equal power within the branches. the "check" meant that one branch would watch one branch and "balance" them if they were too powerful. if you want more info on this, i would just google checks and balance system.