Read the passage and answer the question based on it.
As the climate in the Middle East changed, beginning around 7000 B.C. conditions emerged that were conducive to a more complex and advanced form of civilization in both Egypt and Mesopotamia. The process began when the swampy valleys of the Nile in Egypt and of the Tigris and Euphrates Rivers in Mesopotamia became drier, producing riverine lands that were both habitable and fertile, attracting settlers armed with the newly developed techniques of agriculture. This migration was further encouraged by the gradual transformation of the once-hospitable grasslands of these regions into deserts. The human population became increasingly concentrated into pockets of settlement scattered along the banks of the great rivers.
These rivers profoundly shaped the way of life along their banks. In Mesopotamia, the management of water in conditions of unpredictable drought, flood and storm became the central economic and social challenge. Villagers began early to build simple earthworks, dikes, canals, and ditches to control the waters and reduce the opposing dangers of drought during the dry season (usually the spring) and flooding at harvest time.
Such efforts required a degree of cooperation among large number of people, that had not previously existed. The individual village, containing only a dozen or so houses and families, was economically vulnerable; but when several villages, probably under the direction of a council of elders, learned to share their human resources in the building of a coordinated network of water-control systems, the safety, stability, and prosperity of all improved. In this new cooperation, the seeds of the great Mesopotamian civilizations were being sown.
The technological and mathematical inventions, too, were stimulated by life along rivers. Such devices as the noria (a primitive waterwheel) and the Archimedean screw (a device for raising water from the low riverbanks to the high ground where it was needed), two forerunners of many more varied and complex machines, were first developed here for use in irrigation systems. Similarly, the earliest methods of measurement and computation and the first developments in geometry were stimulated by the need to keep track of land holdings and boundaries in fields that were periodically inundated.
The rivers served as high roads of the earliest commerce. Traders used boats made of bundles of rushes to transport grains, fruits, nuts, fibers, and textiles from one village to another, transforming the rivers into the central spines of nascent commercial kingdoms. Trade expanded surprisingly widely; we have evidence suggesting that, even before the establishment of the first Egyptian dynasty, goods were being exchanged between villagers in Egypt and others as far away as Iran.
Similar developments were occurring at much the same time along the great river valleys in other parts of the world - for example, along the Indus in India and the Hwang Ho in China. The history of early civilization has been shaped to a remarkable degree by the relation of humans and rivers.
According to the passage, the increasing aridity of formally fertile grasslands in Egypt and Mesopotamia caused the settlement patterns in those regions to become
" The building of a coordinated network of water-control systems, the safety, stability, and prosperity of all improved" – that is, the civilizations became more concentrated. More concentrated is appropriate.