Insect infestations in certain cotton-growing regions of the world have caused dramatic increases in the price of cotton on the world market. By contrast, the price of soybeans has long remained stable. Knowing that cotton plants mature quickly, many soybean growers in Ortovia plan to cease growing soybeans and begin raising cotton instead, thereby taking advantage of the high price of cotton to increase their income significantly, at least over the next several years.
Which of the following, if true, most seriously weakens the plan’s chances for success?
- The cost of raising soybeans has increased significantly over the past several years and is expected to continue to climb.
- Tests of a newly developed, inexpensive pesticide have shown it to be both environmentally safe and effective against the insects that have infested cotton crops.
- In the past several years, there has been no sharp increase in the demand for cotton and for goods made out of cotton.
- Few consumers would be willing to pay significantly higher prices for cotton goods than they are now paying
- The species of insect that has infested cotton plants has never been known to attack soybean plants
正确答案是B, 但D为何不对. 请赐教! | 
