The correct option is D Over production and fall of agricultural prices
Mechanisation had reduced the need for labour. Production had expanded so rapidly during the war and post-war years that that there was a large surplus. Unsold stocks piled up, storehouses overflowed with grain, and vast amounts of corn and wheat were turned into animal feed. Wheat prices fell and export markets collapsed. This created the grounds for the Great Agrarian Depression of the 1930s that ruined wheat farmers everywhere.