Final answer:
To study the effects of the World Trade Organization on third-world nations, a macro level theory is appropriate as it involves large-scale analysis of groups and institutions at a global level.
Step-by-step explanation:
If someone wanted to examine the effects of the World Trade Organization on third-world nations, they would likely employ a macro level theory to guide research. At the macro level, researchers analyze trends among and between large groups and institutions on the national and/or global scale. Hence, the impact of the World Trade Organization, which affects global trade policies and international relations, would be best examined through a macro-level lens rather than a micro or meso level, which focus on smaller groups and individual interactions or intermediate-sized entities.