Answer
Curve a is the graph of $f$, curve b is the graph of $f''$, curve c is the graph of $f'$.
Work Step by Step
First look at curve b.
Curve b has 3 local extremas (the point where the curve changes from going up to down and vice versa) and 2 times passes the $Ox$ line.
Imagine if curve b represents $f$ or $f'$, there must be another curve that passes the $Ox$ 3 times to match the 3 local extremas of curve b.
However, none of the remaining curves passes the $Ox$ 3 times. Therefore, curve b is the graph of $f''$.
Now look at the remaining 2 curves.
Curve c has 2 local extremas and 1 time passes the $Ox$ line. If curve c represents $f$, then curve a must pass the $Ox$ line 2 times to match the 2 local extremas of curve c.
However, curve a does not pass the $Ox$ line at all. Therefore, curve c is the graph of $f'$ and curve a is the graph of $f$.
