Choice D is the best answer because it maintains agreement between pronoun (“it”) and antecedent (“any one”) and between subject (“any one”) and verb (“occurs”).
Choice A is not the best answer because the plural verb “occur” does not agree with the singular subject “any one.”
Choice B is not the best answer because the plural verb “occur” does not agree with the singular subject “any one” and because the plural pronoun “they” does not agree with the singular antecedent “any one.”
Choice C is not the best answer because the plural pronoun “they” does not agree with the singular antecedent “any one.”