The curve $\mathscr{C}$ below represents a function $f$ defined and twice differentiable on $]0; +\infty[$. We know that:
- the maximum of the function $f$ is reached at the point with abscissa 3;
- the point P with abscissa 5 is the unique inflection point of the curve $\mathscr{C}$.
We have:
A. for all $x \in ]0; 5[$, $f(x)$ and $f'(x)$ have the same sign;
C. for all $x \in ]0; 5[$, $f'(x)$ and $f''(x)$ have the same sign;
B. for all $x \in ]5; +\infty[$, $f(x)$ and $f'(x)$ have the same sign;
D. for all $x \in ]5; +\infty[$, $f(x)$ and $f''(x)$ have the same sign.