8. If \( f \) is a differentiable function, then \( f'(1) \) is given by which of the following?
I. \( \lim\limits_{{h \to 0}} \frac{f(1+h) - f(1)}{h} \)
II. \( \lim\limits_{{x \to 1}} \frac{f(x) - f(1)}{x - 1} \)
III. \( \lim\limits_{{x \to 0}} \frac{f(x+h) - f(x)}{h} \)
