f(x) = 21x4 + Ax3 + Bx2 + Cx - 9, where A, B, C are integers. The list of all potential rational zeroes of f (a ) is: O1 {1, 3, 9, 3, 7, 27 } O 1 {1, 3, 7, 9, 21} O # {1, 3, 9} O + {1, 3, 7, 21} OH{1, 3, 7, 21, 1 7 1 7 O 1 {1, 3, 9, 1, 1 3 9 17 3 1 7 , 7 1 71 21 1