This is a weaken question. The shift from the first sentence to the second makes the assumption clear. The argument relies on the underlying claim that, because wind power produces the fewest pollutants, it is the best choice. More probably, there are other considerations. The correct choice will likely point out some other consideration that may outweigh the level of pollutants.

(A) A reference to an earlier (or different) report is almost always wrong; we have no way of comparing the validity of the two reports. Anyway, it doesn't address the assumption.
(B) The level of government investment is similar to a separate report, as in (A). If anything, it strengthens the claims of wind power supporters, but to be a strengthener, we must assume that the government is making a valid choice.
(C) This is correct. This is a strong reason why wind power may not be the best choice for new rural areas.
(D) This is an irrelevant comparison. The evidence in the argument compares wind power to other green energy alternatives. If anything, this point strengthens the argument, but not very effectively.
(E) The frequency of reports has no effect whatsoever on the argument.