(a) lowest frequency that can return back to earth at any angle of beaming
(b) highest frequency that can return back to earth at any angle of beaming
(c) lowest frequency that can return back to earth to 90° angle of beaming
(d) none of the above
(b) highest frequency that can return back to earth at any angle of beaming
(c) lowest frequency that can return back to earth to 90° angle of beaming
(d) none of the above