OE
The correct response for the first blank cannot be determined without considering the second sentence. The correct choice for the second blank, however, can be determined more readily. Neither Choice D, “redundant,” nor Choice F, “understated,” makes sense when coupled with the preceding “impressive but.” Since the figures were “used by opponents to tar the whole idea,” Choice E, “unsound,” is the word that makes the most sense in this context.
Once “unsound” is selected for the second blank, it follows that “confirmed” cannot be correct for the third blank. And if the figures were “used by opponents,” then they cannot have been “ignored.” Since the figures were unsound, it is natural that they would later be “discredited.”
Now that the figures have been characterized as unsound and discredited, it is possible to identify the correct response for the first blank. From the second sentence it is clear that the process of putting a cash value on the ecological services provided by nature is neither “dispassionate” nor “straightforward.” It is instead “problematic.”
Thus, the correct answer is problematic (Choice B); unsound (Choice E); and discredited (Choice H).