Woran erinnern die sogenannten „Stolpersteine“ in Deutschland?

What do the so-called 'Stolpersteine' in Germany commemorate?

Explanation

The correct answer is "an die Opfer des Nationalsozialismus" because it matches the German civic, legal, historical, or institutional fact asked in this question, specifically the topic of Stolpersteine. The other options do not fit the question correctly.