后来，他们学会了按季节耕作，适时播种，以及在干旱地区利用每年的洪水来灌溉他们的农田。

Later, they learned to work with the seasons, planting at the right time and, in dry areas, making use of annual floods to irrigate their fields.

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干旱地区需要灌溉才能使作物生长。

Irrigation is needed to make crops grow in dry regions.

《新英汉大辞典》

旱地农业，灌溉农业和牛羊牧业是美国西部大平原地区的主要活动。

Dry farming, irrigation farming, and the cattle and sheep herding are the main activities of the Great Plains of the American West.

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