Which statement best explains how classical civilizations developed out of the first agricultural societies?
a. the need to defend surplus food supplies and permanent settlements provided incentives to develop greater military power.
b. the improvements in productivity in early agricultural societies enabled more complex societies to develop.
c. the need for population control in rapidly growing agricultural societies led to important changes in political and religious doctrines.
d. increases in food production allowed early agricultural societies to devote most of their resources of food