How do curves a and b compare to each other with respect to f and f ′?

Hmm, we see that the red line intersects the x axis at around the same place where the concavity of the blue line changes

so i would say that the blue line is f(x) and the red line is f''(x)



if the red line was a derivitive of the blue line, it should intersect the x axis at about x=0 and x=0.9 which it doesn't

they aren't derivitives of each other

3rd option

None of the options you showed are it.