After the Second World War, the charter of the newly formed United Nations established an eleven- member Security Council and charged it with taking collective action in response to threats to world peace. The charter further provided that the five nations that were then the major powers would permanently have sole authority should be required to assume the burden of enforcing a decision it found repugnant.
What this question is testing
Conclusion
The author treats the rationale as supporting permanent veto authority for the five nations that were major powers when the UN was founded.
Evidence
The reasoning: major powers bear the enforcement burden, and no nation should be forced to enforce something it finds repugnant.
Evaluate
Watch the time problem. The reasoning would naturally extend to any nation that becomes a major power — they'd also bear enforcement burden and deserve a veto. But the structure freezes the list at the founding moment. The argument quietly assumes no other nation will later rise to major-power status — otherwise the rationale would justify giving them a veto too, and the "permanent sole authority" arrangement falls apart.
Goal
The right answer establishes that no future nation would join the major-power club. Negate it (some new nation does become a major power) and the reasoning no longer supports permanent sole authority for just the original five.
Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.