A president and a treasurer are to be chosen from a student club consisting of 25 people. How many different choices of officersare possible if; ( ⅰ ) there are no restrictions;（ⅱ） A and B will...

A president and a treasurer are to be chosen from a student club consisting of 25 people. How many different choices of officers are possible if; ( ⅰ ) there are no restrictions; （ⅱ） A and B will serve together or not at all; （ⅲ） C and D will not serve together