There is a close call and I will go for C.

Reason: Assuming soyabeen base is significant and the fact that last several years has not seen large demand of cotton and related product, it will not be wise if soyabeen producer goes for cotton as once new supply will come the cotton prices will fall...something like...lalach me dono gaye maya mili na ram..

Tough call between B and C.
I would have chosen B as well.
In C, it says no increase in demand over the last few years, whereas argument says profits over the next few years.

not sure what the correct answer is.

What is OA ?

Amongst all the answer choices C seems to be the best.

B)Counters the main part of the causal-relationship. i.e. when infestation increase-price increase. Now this price increase does not mean that "demand" of the cotton increase. The potential market of the cotton could remain same but due to the infestation less cotton is available in the market and hence price increase. This answer choice affect the information/premise given in the statement.

C) Answer C seems to affect the plan of Soybean Grower. Since there is not sharp increase in the deman of the cotton, growing more cotton and supplying more cotton in the market would bring down the prices. This will go against the plan. C looks to be a better answer choice.

Whats the OA?

IMO B

The reason soyabean planters planned to enter cotton business started from the motivation that prices of cotton have been rising.

The price rise of cotton may happen because of any of these causes:
1. The orginal problem of insect infestation caused the price rise.
2. Alternate cause , increase in demand ,caused price rise.

In this particular case , cause 1 seems to be more probable because the premise says this as the motivation behind soybean planters' decision to move to cotton farming . So negating that would weaken more.

The main assumption that the price would continue to remain high is most weakened when the cause due to which the prices of cotton were high does not remain. i.e when a new pesticide is available and that can rectify the problem. This would lead the prices to come down again.

Demand seems to be out of scope in this case.

Please correct me if anyone feels its not making sense.

My intuition whispers that it is C.