standards under subsection (a) or the enhanced energy efficiency and conservation standards and green building standards under subsection (b), or both, with respect to any covered federally assisted housing described in paragraph (3)(A) or any HUD assistance. (2) Rural housing The Secretary of Agriculture may, by regulation, provide for the applicability of the energy efficiency standards under subsection (a) or the enhanced energy efficiency and conservation standards and green building standards under subsection (b), or both, with respect to any covered federally assisted housing described in paragraph (3)(B) or any assistance provided with respect to rural housing by the Rural Housing Service of the Department of Agriculture. (3) Covered federally assisted housing For purposes of this subsection, the term covered federally assisted housing means— (A) any residential or nonresidential structure for which any HUD assistance is provided