Factor the following expressions fully: ( f(x) = x³ - x2- 9x + 9 )
a) ( (x-3)(x+1)(x-3) )
b) ( (x+3)(x+1)(x-3) )
c) ( (x-3)(x-1)(x+3) )
d) ( (x+3)(x-1)(x-3) )