What is the essence of the argument?
Genetically modified seeds are highly resistant to insects. But they are more expensive and need more fertilizer and water. So farmers won't save money by using them (prediction).
But people like them so their use will keep increasing (conclusion).

So what part is in bold? Let me underline it to show clearly...

Genetically modified seeds are highly resistant to insects. But they are more expensive and need more fertilizer and water. So farmers won't save money by using them (prediction).
But people like them so [i]their use will keep increasing (conclusion)

(A) The first supplies a context for the argument; the second is the argument's main conclusion.
Wrong - second is not the main conclusion

(B) The first introduces a development that the argument predicts will have a certain outcome; the second is a state of affairs that the argument denies will be part of that outcome.
Wrong - the second is not related to the outcome at all. It cannot accept or deny whether it is a part of that outcome

(C) The first presents a development that the argument predicts will have a certain outcome; the second acknowledges a consideration that weighs against that prediction.
Wrong - second is not a consideration against the prediction. Prediction is about saving money by using modified seeds. Just because people like modified seeds, farmers won't save money by using them i.e. the cost will not go down. Note that the revenue farmers earn may increase because people like these seeds but the cost of using them will not decrease.

(D) The first provides a certain outcome that the agrument seeks to weigh against; the second is a consideration that support the main conclusion.
Correct.

(E) The first and the second each provide evidence to support the argument's main conclusion.
Wrong - First does not provide evidence to support conclusion

Answer: B