In the following reaction, how is the rate of appearance of the underlined product related to the rate of disappearance of the reactants?

A) It is equal to the rate of disappearance of one of the reactants.
B) It is half the rate of disappearance of one of the reactants.
C) It is twice the rate of disappearance of one of the reactants.
D) It is unrelated to the rate of disappearance of the reactants.