<em>D. Annual floodwaters in the Nile delta washed silt inland to build up the soil
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<u>Explanation:</u>
The Crescent was boomerang-shaped areas of the middles. It is the easiest and was a home of most comfortable human civilization. It is also known as the cradle civilization. The city gave rise to many technological innovations including agriculture, wheel, and writing as well as irrigation. The crescents also included the ancient Mesopotamia.
However, the Fertile Crescent is not as fertile as it was in the beginning during the 1950s. There has been a diversion of large scale irrigation away from the Tigris and the river systems.
