Tough and Tricky questions: Functions.
For which of the following functions f(x) is the relation f(f(x)) = f(f(f(f(x)))) NOT true for at least some values of x not equal to zero?
A. f(x) = -|x|
B. f(x) = 2 - x
C. f(x) = 3x
D. f(x) = \frac{4}{x}
E. f(x) = 5
Kudos for a correct solution.