(a) Any product similar to the commercial product but modified or altered in compliance with specified Government requirements and, as such is usually sold only to the Government and not through the normal catalog or retail outlets;

(b) Any product similar to a commercial product that is either assembled or manufactured in accordance with specifically stated Government requirements and sold only to the Government and not to the general public; or

(c) A commercial product identified or marked differently than the commercial product normally sold to the general public.