Which statement best describes how to determine whether f(x)=9-4x^2 is an odd function?
a. determine whether 9-4(-x)^2 is equivalent to 9-4x^2
b. determine whether 9-4(-x^2) is equivalent to 9+4^2
c. determine whether 9-4(-x)^2 is equivalent to -(9-4x^2)
d. determine whether 9-4(-x^2) is equivalent to -(9+4x^2)