There are 10 possible ways to select a president from the club, because their are 10 available members to choose from.
After a president is chosen, their are 9 possible ways to select a vice president, because one of the members will already have the position of president, so they can't be vice president (10-1=9)
Now we just multiply to possibilities of presidents by the possibilities of vice-presidents.
president*vicepresident=
10*9=90
Answer= D. 90