Egyptian civilization was centered along the . Agriculture flourished, because the river each June, leaving behind , which had the nutrients needed for plants to grow bigger and stronger. Egypt's main crops were papyrus, used to make , and barley, used to make .

The river’s annual flooding left behind rich alluvial soil, which contains nutrients that help crops grow. That makes “rich alluvial soil” the phrase that fits the blank about what the river left behind. The other choices do not describe nutrient-rich soil.

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