Which led to dust storms during the 1930s?

Dust storms during the 1930s were caused by drought combined with extensive farming. Plowing and planting removed native grasses that had held the soil in place, and the drought dried out the exposed soil so strong winds could carry it away. Therefore, “farming and drought” is correct; heavy rains would not have created the dry conditions behind the storms.

AI-written and checked against the verified answer.