I think you are getting far too caught up in this whole gradable/non-gradable issue. You can keep asking us the same questions over and over again. You will keep getting the same answers. Adjectives are clearly marked as gradable or non-gradable in good dictionaries. You should follow those rules in exams and in important formal situations. You should also be ready to hear native speakers take absolutely no notice of those "rules" in everyday speech and add "very" (or similar words) to supposedly non-gradable adjectives.
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