Which statement best describes how to determine whether f(x) = x³ - 5x + 1 is an even function?
a) Determine whether f(-x) is equivalent to f(x).
b) Determine whether (-x)³ - 5(-x) + 1 is equivalent to x³ - 5x + 1.
c) Determine whether f(x) is equivalent to -f(x).
d) Determine whether (-x)³ - 5(-x) + 1 is equivalent to -x³ - 5x + 1.