Consider the following three-step representation of a reaction mechanism.

step 1: a + b --> ab (fast) and the rate = k[a][b]
step 2: ab + b --> ab2 (slow) and the rate = k[ab][b]
step 3: ab2 + b --> ab3 (fast) and the rate = k[ab2][b]
overall: a + 3b --> ab3 and the rate = k[a][b]2

which explains why the rate law for the overall equation is not the same as the rate equation for the rate-determining step?
a; the fastest step determines the overall rate law.
b: the overall rate law is determined from the balanced equation.
c: ab is an intermediate; therefore the rate law is determined from the reactants in the previous step.
d: b is an intermediate; therefore the rate law is determined from the reactants in the previous step.