(A) captures the main point well. The author wrote the passage to tell us that the evidence in favor of the environmentalists’ claims is weak.

This goes too far. The author never says that international debt does not lead to environmental damage. She only says that the evidence in favor of the claim that it does lead to environmental damage is weak. In other words, the author thinks it’s not yet established that international debt leads to environmental damage, but isn’t denying the possibility that it does.

Also, even if (B) were supported, it would be too narrow to be the main point. The issue of environmental damage is only one of the reasons the environmentalists believe that international debt lowers a nation’s quality of life. The author’s point is about the environmentalist’s claim about quality of life – any dispute about environmental damage only supports the broader conclusion criticizing the claim about quality of life.

(C) isn’t supported by the passage, so it can’t be the main point. The author never said that further study “will” demonstrate that the environmentalists are wrong. The author simply points to the lack of evidence in favor of their view and the existence of some evidence that doesn’t support their view. The author never claims anything about what future studies will reveal.

(D) doesn’t accurately describe the author’s view about the environmentalists’ claims. The author says that the evidence in favor of their claims is “weak.” The author does not suggest that the environmentalists misunderstand economic theory. The author of the passage could believe that the environmentalists do understand economic theory accurately, but are simply making arguments based on unpersuasive evidence.

(E) is both too narrow and inaccurate. It’s too narrow, because even if the author agreed with (E), it would simply be a supporting point for the overall conclusion that the environmentalists’ claims about the relationship between international debt and quality of life are wrong. Environmental damage is simply one aspect of quality of life that the passage discusses, but there were aspects, too.