The matching is: $$a\to C,\quad b\to C,\quad c\to A,\quad d\to B.$$
Work Step by Step
The only decreasing function is $c$ so it has to be matched with the only negative derivative $A$. The rest of the functions are increasing and the bigger the rate of increase (the steeper they are) the bigger the derivative. The functions $a$ and $b$ are parallel so they have to be matcher with the same derivative and it is $C$ (because we see that the value of $b$ increases by one unit when $x$ changes by $1$). This leaves $d$ to be matched to $B$.