Some of them undoubtedly made use of the fertile alluvial soil left by rivers after the flood season, but this simple method of agriculture is not thought to be productive enough to support cities.

• 他们中的一些人毫无疑问是利用洪水季节过后由河流留下来的肥沃冲积土壤，但这种简单的农艺模式并不足以生产出足够食物来支持城市。