Which level of government held a majority of the responsibility under the articles of confederation?

The best I can give you is this. Under the Articles of Confederation, power was centered in Congress. They held the majority of responsibility. If you need some more on that I'd skim this. >
https://blogs.loc.gov/law/2011/09/the-articles-of-confederation-the-first-constitution-of-the-united-states/

Iwould pick a true