Universal Stumpers VIII by Sijnaanik

Question 5

For most of the 13th through 17th centuries, The King of Bohemia, The Count Palatine of the Rhine, The Duke of Saxony, The Margrave of Brandenburg, and the Archbishops of Mainz, Trier, and Cologne, were the seven people who comprised what group?

Prince-electors of the Holy Roman Empire (or anything reasonably close to this)