Choose the best reason that the function $f(x) = x^{75}+x^{33}+x^{3} + 16$ has neither a local maximum nor a local minimum.

(a) The function $f(x)$ is always positive.
(b) The derivative $f'(x)$ is always negative.
(c) The derivative $f'(x)$ is always positive.
(d) The highest power of $x$ in $f(x)$ is odd.

Answer:

Note: Input a, b, c, or d .