A. if the cost of raising soybeans has increased significantly, then farmers are more likely to give up soybean raising and turn to cotton, which price has risen lately. so this answers supports the assumption.
B. irrelevant!! nothing concerned with newly developed and inexpensive insecticide in the argument.
C. the premise for the growing demand for cotton is "In the past several years
". but the argument's assumption is concerned with "at least over the next several years
". that means the past conditions dont necessarily affect the future conditions.
D. if few customers would be willing for pay more for cotton goods, then the price of cotton is not likely to increase.
live and love like you never hurt.