The answer is C.

Option C is chosen because "unimpeachable" captures the idea that providing funding for fertilizer seems flawless or beyond criticism initially, but the subsequent revelation of troubling questions adds a layer of unexpected complexity.

A. Imprudent: Imprudent means lacking discretion or good judgment. Providing funding for fertilizer may seem imprudent because, upon closer examination, troubling questions arise. This option suggests that the decision to fund fertilizer lacks wisdom.
B. Expensive: Expensive means costing a lot of money. While providing funding for fertilizer might be costly, this option doesn't capture the nuanced contrast in the sentence, which indicates that there are troubling questions upon closer examination of the data.
C. Unimpeachable: Unimpeachable means beyond reproach or unable to be criticized or doubted. In the context of the sentence, providing funding for fertilizer may seem unimpeachable initially, suggesting that it appears flawless or beyond criticism. However, the latter part of the sentence introduces the twist that closer examination raises troubling questions. The use of "unimpeachable" here underscores the unexpected nature of the issues that arise despite the initial appearance.
D. Modern: Modern means relating to the present or recent times. This option doesn't seem to connect well with the sentence's theme about soil fertility problems and troubling questions arising from closer data examination.
E. Worrisome: Worrisome means causing anxiety or concern. While this option does convey the sense of concern, "unimpeachable" is chosen as the answer because it adds an additional layer by suggesting that the initial perception of flawlessness is later challenged by troubling questions.