Irrigation made it possible for the civilization known as Sumer to arise on the Mesopotamian plain in the fifth millennium B.C.E. A. The scarcity of natural resources on the plain made it necessary for a powerful elite to emerge and take charge of trade and imports. B. The economy of each city was based on a craft such as pottery or metal working, and the city of Eridu was known for its saws, scythes and weapons. C. Writing appeared in the form of logograms and later developed into a system using signs to represent syllables rather than whole words. D. Priests were powerful figures in the ancient civilization and controlled the political and economic life of the cities. E. The earliest city states had one or more patron gods and were built around central temple complexes. F. The development of the wheel and the creation of bronze were important innovations in Sumer