The Secretary may reject an Indian Tribe's final offer for one of the following reasons:
(a) the amount of funds proposed in the final offer exceeds the applicable funding level to which the Indian Tribe is entitled under the Act;
(b) the PSFA that is the subject of the final offer is an inherent Federal function that cannot legally be delegated to an Indian Tribe;
(c) the Indian Tribe cannot carry out the PSFA in a manner that would not result in significant danger or risk to the public health; or
(d) the Indian Tribe is not eligible to participate in self-governance under section 503 of the Act [25 U.S.C. 458aaa-2].