The possible rational zeros of polynomial function [tex]f(x) = x^4 + 2x^3 - 3x^2-4x + 20[/tex] could be only among the divisors of the free term of this polynomial function.
The free term is 20 and the divisors of 20 are:
[tex]\pm 1, \pm 2, \pm 4, \pm 5, \pm 10, \pm 20.[/tex]
Answer: correct choice is C