The regulations may prescribe—
(a) persons of a specified class to be contractors for the purposes of this Act or the regulations or specified provisions of this Act or the regulations;
(b) persons of a specified class not to be contractors for the purposes of this Act or the regulations or specified provisions of this Act or the regulations;
(c) contracts of a specified class to be regulated contracts for the purposes of this Act or the regulations or specified provisions of this Act or the regulations;
(d) contracts of a specified class not to be regulated contracts for the purposes of this Act or the regulations or specified provisions of this Act or the regulations.