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A minor note: they are not articles, but just indicative pronouns. We do not have articles (a/the) in Russian.



BTW, to simplify your task:
1. All nouns derived from verbs with the suffix...

Then it is probably "прочный портфель" (durable). This adjective is used for solid bodies in physical sense. "Стойкий" does not work here.

твердая сталь - ОК
сбалансированная справедливость - ОК, but too "scientific". Many people would hardly get the idea what it means :) Try to find a simpler adjective :) e.g. всеобщая справедливость...