(A) is too narrow. Although the author does suggest that cuts in domestic spending might stop implementation of harmful programs, which arguably could help a nation’s quality of life, this is just one supporting point in the second paragraph. It’s made in support of the broader point that the environmentalists’ arguments are not supported by strong evidence.

(B) is a great fit for what we could anticipate. The primary purpose of P2 is to criticize the environmentalists’ arguments.

The author is open to more studies that investigate this relationship. But (C) is not the primary purpose of the second paragraph. The lack of sufficient studies is merely one point in support of the broader criticism of the environmentalists’ arguments.

The author does not argue that there isn’t a relation between international debt and a nation’s quality of life. The author merely said that the relationship is currently unknown.

The author criticizes the evidence for the environmentalists’ claims. But that’s not the same as “questioning the sources” of the evidence. The author never comments on who provided the evidence, who conducted or reported the studies, or who is otherwise responsible for the evidence.