For a reaction proceeding, concentration of reactants decreases over time while products increase. The rate of change is highest initially and slows as reactants deplete. Thus, reactant concentration graphs show a decreasing curve that flattens, while product graphs show an increasing curve that levels off. The correct graph must depict this non-linear behavior, not a straight line.

For a first-order reaction: $\left[A\right]=[A{]}_0{e}^{-kt}$, an exponential decay.

Final Answer: The graph showing a curved decrease for reactant concentration (or curved increase for product) that asymptotically approaches a limit.