GMAT真题里面的一道题目，请大家指教一下哦

GMAT真题里面的一道题目，请大家指教一下哦答案是B，我觉得C好象比较好？

Q40:

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?

1. The cost of raising soybeans has increased significantly over the past several years and is expected to continue to climb.
   
2. 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.
   
3. In the past several years, there has been no sharp increase in the demand for cotton and for goods made out of cotton.
   
4. Few consumers would be willing to pay significantly higher prices for cotton goods than they are now paying.

    E.  The species of insect that has infested cotton plants has never been known to attack soybean plants.

从表面上看c,d都是讲棉花没有市场需求，所以swich from soybean to棉花不会有利益

C不正确在于：时间状语是In the past several years，和要削弱的结论发生的时间段不符合

D不正确在于：d的削弱是在假设原结论成立条件后的削弱，即已经默认了棉花价格的肯定升高而不是在原来条件下的，所以也不是对结论的削弱

请指教。

C是过去的，可以讲是无关；

另外，文章在讲供给的问题，害虫---->供给,杀虫药－－>害虫---->供给