Answer:
A. Levees held back the annual floods of the Tigris and Euphrates Rivers.
B. Surplus barley and wheat could be traded for other things.
Explanation:
The Sumerians were a group of people who lived in ancient Mesopotamia, nowadays southern Iraq. This is the first culture that we know of in Mesopotamia, which is considered the "cradle of civilization." Therefore, they were one of the first civilizations in the world. Sumerian agriculture and trade were very developed. Farmers were able to grow grain and other crops through the use of levees that held back the floods. They also developed a system of irrigation.
