For which of the following functions f is

For which of the following functions f is f(x) = f(1-x) for all x?
f(x) = 1-x

f(x) = 1-x^2

f(x) = x^2 - (1-x)^2

f(x) = x^2(1-x)^2

f(x) = x/1-x

since the problem stattement defines the f'n to be true for all x, we can define x=1
Hence for which f'n ....f(1)= f(0) ?
a: f(0) = 1, f(1) = 0. nope

b: f(0) = 1, f(1) = 0. nope

c: f(0) = -1, f(1) = 1. nope

d: f(0) = 0, f(1) = 0. looks good

e: f(0) = 0, f(1) = undefined. nope