We have that this reaction can go both directions, depending on the proportions of reactants A & B and that of the product C. Nonetheless, since initially we only put in reactants A and B, some of these molecules will react to form molecule C. Thus, at the start we have that C has zero concentration and the concentration of B is higher than the concentration of A (B has 2 moles in the container, A has 1). We see that gradually the concentration of A and B drop (by the same amount since each reaction needs 1 molecule of A and 1 molecule of B) and that due to the newly created C molecules, the concentration of C rises. In the end, we get to an equilibrium situation where every molecule has non-zero concentration and the curves become flat. Given the above analysis, the correct answer choice is A. In all cases the curve of A will become lower since some of it will react with some B to form C
