Which statements are true about the function f(x) x³ - 4x?
a. The function has a relative minimum between x = -2 and x = 0.
b. The function has a relative minimum between x = 0 and x = 2
c. The function has a relative maximum between x = -2 and x = 0
d. The function has a relative maximum between x = 0 and x = 2