Answer:
D.irrigation ditches and canals
Step-by-step explanation:
The Tigris and the Euphrates follow roughly parallel courses as they flow from the highlands of eastern Turkey through Syria and Iraq and into the Persian Gulf. The rivers flooded the area every spring when snow from nearby mountains melted and made its way into their currents. Little by little the cities that were adjacent to the rivers managed to produce enough food to trade with other settlements.
Hopefully this helps you!