The correct answers are A) Flatland with poor drainage led to salinization from irrigation waters and C) It was located on a flat plain that made it vulnerable to attack.
The geographic characteristics that were factors in the decline of Sumer were flatland with poor drainage led to salinization from irrigation waters and it was located on a flat plain that made it vulnerable to attack.
Sumer was the oldest civilization known to man. It settled in the Middle East region, between the Tigris and Euphrates Rivers, of what today is Iraq, approximately 6,000 years ago. It became a great and prosperous civilization that based its power in city-states such as Nippur, Lagash, Kish, Uruk, and Ur. Unfortunately for them, political conflicts, territorial differences, and greed started to affect the relationship of these city-states, a situation that combined with poor drainage that led to salinization from irrigation waters and the invasion from enemies.