Concept:FEDECO (Federal Electoral Commission) was the independent body set up to organise and supervise Nigeria's elections.Explanation:Political parties themselves established their own party offices, so option A is not correct.The Federal Military Government promulgated the 1979 constitution into law, not FEDECO, making option B wrong.Elected officials were sworn in by the Chief Justice, Chief Judges, or Speakers of the state Houses of Assembly, so option C is also incorrect.One of FEDECO's major functions was to divide the country into clear electoral areas for the elections.This process is known as delineating electoral constituencies, which makes option D the correct answer.Answer:D. delineating electoral constituencies.