Answer:
B). The land in river valleys supported agriculture.
Step-by-step explanation:
The main reason why the first civilizations developed in river valleys was because the land in these valleys supported agriculture. Land in these regions tends to be very fertile, for several reasons. The land in these areas is often full of nutrients, as the river carries them when it overflows. Moreover, the proximity of water makes it easier to irrigate the crops. Finally, water usually brings a larger amount of animals, which in turn help nourish the ecosystem.