A student made a graph plotting the progress of a reaction over time. The student forgot to label the y-axis of the graph.
What best explains the label that the student should use on the y-axis?

A. Amount, because as the amount of product decreases, the amount of reactant increases over time.

B. Reaction rate, because forward and backward reaction become equal at equilibrium.

C. Amount, because the amounts of reactants and products become constant after equilibrium is reached.

D. Reaction rate, as the rate of forward reaction increases and rate of backward reaction decreases over time.