According to the passage, one of the striking features of the three great rivers of the Middle East, is that ____ .

It is the opinion of most archaeologists that
civilisation first developed in the Middle East, where,
of all the regions in the world, natural conditions
offered the greatest assistance to man in his
changeover from a life of nomadic wandering as a
hunter to settled occupation of the soil. The regular
rise of the three larger rivers, Nile Euphrates, and the
Tigris; annual renewal of soil fertility by the deposition
of a layer of silt; and the generally warm climate,
favourable both to the growth of a rich plant-life, and
to the activities of man himself, were all special
inducements to the adoption of a way of life based on
agriculture.