Which of the following was an effect of farming on the development of early river valley civilizations?

a. surplus food allowed groups of people to specialize and stratify, which led to laws and governments.

b. farming produced little food, so people developed government to determine how to distribute crops.

c. because farming produced extra food, people were able to form less permanent settlements.

d. as farming proved to be too difficult, many people needed to hunt animals and gather wild plants.