When we read the question, the prompt gives a plan, and the question stem asks us to cast doubt on the plan. We care about whether or not domestic agriculture improves in competitiveness. So we can use that as a basic prediction and ask of each answer choice, "does or could domestic agriculture still improve in competitiveness?"
Testing this prediction, choice (A) is irrelevant, because the domestic agriculture could still improve in competitiveness; the plan doesn't have a deadline. Choice (B) tells us that competitors might still have an advantage. But even then, the domestic agriculture may be in a better relative position that it was before; the gap has narrowed; it has improved. So (B) is out. Choice (C) looks promising; if domestic farmers pocket the money, domestic agriculture does not become more competitive. So choice (C) stays in. (D) is hardly great news, but the domestic agriculture could still improve in competitiveness. So (D) is out.
We eliminate (E), also, since (E) raises considerations immaterial to whether the plan will work. We're left with (C).
We can look for logical confirmation of the correct answer: we can apply the negation test to (C). If we negate (C), domestic producers of agriculture have lots of incentive to use the subsidies to invest in agrarian technology. In that case, the expectation that domestic agriculture would improve in competitiveness is strengthened. The fact that the negated (C) is a strengthener confirms that non-negated (C) is a weakener.
The correct answer is (C).