(a) If there is only one day school, on-reservation boarding school, or peripheral dorm within a reservation's boundaries, the Secretary will establish the reservation boundary as the geographic attendance boundary;

(b) When there is more than one day school, on-reservation boarding school, or peripheral dorm within a reservation boundary, the Tribe may choose to establish boundaries for each;

(c) If a Tribe does not establish boundaries under paragraph (b) of this section, the Secretary will do so.