Consider that the graph of f(x) is the graph of a cubic function, that is, the graph of a 3 degree polynomial. If you apply first derivative to such a polynomial, the result is another polynomial of degree 2.
Now, take into account that the graph of a polynomial of degree 2 is a parabola. The parabola can open up or down. It depends of the leadding coefficient of the polynomial. In this case, due to the graph of f(x), the leadding coefficient is positive, which means that the parabola of f'(x) opens up.
Hence, you can conclude that the graph of f'(x) is option C.