An implication is something NOT stated that can be reasonably concluded from what is stated. The author of the passage implies that _________.

All these early civilizations with irrigation systems probably didn’t just happen to arise alongside rivers. The rivers, the author implies, were the source of water for the irrigation system of each civilization. An implication is something not stated, so eliminate all the statements that are explicitly stated in the passage. This includes (The development of irrigation systems is related to the development of civilizations), and (Irrigation produced the population density needed for civilization to develop), which were explicitly stated in different wording. Answer (The Sumerians were the first to develop civilization because they had two rivers in their valley (the Tigris and Euphrates)) doesn’t seem to be something the author is implying because there’s no development of—or apparent reason for—the idea that two rivers are better than one. The development of trade was an important factor that helped advance and spread early civilizations. Besides providing products a region may not have access to itself, trade allows regions to specialize in products they can produce best, thus increasing overall production.