In which year did nelson mandela retire voluntarily from presidency

What two different approaches did the knights of labor and the american federation of labor take in building a union organization? a) the knights of labor accepted only unskilled workers; the american federation of labor accepted only skilled workers. b) the knights of labor accepted skilled and unskilled workers; the american federation of labor accepted only skilled workers. c) the knights of labor refused to accept african american or chinese workers; the american federation of labor accepted all workers. d) the knights of labor accepted workers from a single industry; the american federation of labor accepted workers from several industries.