Consider a twofactor experiment in which one factor is regio

Consider a two-factor experiment in which one factor is “region” (three regions are used in the study). Give a set of circumstances under which regions would be considered fixed, and a set of circumstances under which it would be considered random. I know what is fixed and random factors (plz don\'t explain that), but I don\'t know how can I come up with examples for this question. (I need examples )

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