Final answer:
The incorrect factor listed as a cause of the Dust Bowl is B. decreasing American demand for farm produce. The actual contributing factors were overcultivation, unfavorable weather conditions, and poor farming techniques.
Step-by-step explanation:
The Dust Bowl was caused by a combination of factors that together created the severe environmental conditions experienced in the 1930s. Notably, one choice in the list did not contribute to the Dust Bowl's conditions:
B. decreasing American demand for farm produce
This was not a factor in causing the Dust Bowl. Instead, the primary causes were A. previous overcultivation of farmland, C. unfavorable weather conditions, and D. poor farming techniques concerning irrigation and crop rotation. The demand for farm produce was not an issue that led to the ecological disaster; rather, the ways in which the land was managed and the natural climate fluctuations played significant roles.