The correct option is D Boorish
A boorish person is rough and bad-mannered. For example, "The hometown fans acted in such a boorish way toward the visiting team that they had to forfeit the game." Hence, Option C is correct. Among the rest of the options, rustic means relating to the countryside, naive means (of a person or action) showing a lack of experience, wisdom, or judgement, barbarian means (in ancient times) a member of a people not belonging to one of the great civilizations (Greek, Roman, Christian). These options do not express this meaning, hence incorrect.