; and (iii) the term particular social group means, without any additional requirement not listed below, any group whose members— (I) share— (aa) a characteristic that is immutable or fundamental to identity, conscience, or the exercise of human rights; or (bb) a past experience or voluntary association that, due to its historical nature, cannot be changed; or (II) are perceived as a group by society. (D) (i) The burden of proof shall be on the applicant to establish that the applicant is a refugee. (ii) To establish that the applicant is a refugee, persecution— (I) shall be on account of race, religion, nationality, membership in a particular social group, or political opinion; and (II) may be established by demonstrating that— (aa) a protected ground is at least one reason for the applicant’s persecution or fear of persecution; (bb) the persecution or feared persecution would not have occurred or would not occur in the future but for a protected ground