请教一道有争议的逻辑题。

Scientists have made genetic modifications to cotton to increase its resistance to insect pests. According to farmers’ report, the amount of insecticide needed per acre to control insect pests was only slightly lower for those who tried the modified seed than for those who did not. Therefore, since the modified seed costs more than ordinary seed without producing yields of higher market value, switching to the modified seed would be unlikely to benefit most cotton farmers economically.
Which of the following would it be most useful to know in order to evaluate the argument?
A. Whether farmers who tried the modified cotton seed had ever tried growing other crops from genetically modified seed.
B. Whether the insecticides typically used on ordinary cotton tend to be more expensive than insecticides typically used on other crops.
C. Whether for most farms who grow cotton it is their primary crop
D. Whether the farmers who have tried the modified seed planted as many acres of cotton, on average, as farmers using the ordinary seed did.
E. Whether most of the farmers who tried the modified seed did so because they had previously had to use exceptionally large quantities of insecticide.

做PREP时候系统给的答案是B，所以我不怀疑其正确性。
以下是我的思路请大家帮看一下对不对：
【题干】转基因种子有抗虫性，但是实践发现转基因棉花种子所用杀虫剂只比普通棉花种子少一点，而前者的价格要比后者高同时产量不变。那么要不要使用这种转基因种子呢？
【B】考察是否给棉花种子用的杀虫剂要比给其他农作物用的贵？假设很贵，那么即使只是少用一点农药，也能省不少钱。（对）
【E】考察是否大多数尝试使用转基因种子的人以前使用了大量的杀虫剂？假设大量使用，但由于不知道杀虫剂的价格，所以无法判断。（错）