Thanks for approving our work . We appreciate your comments and suggestions. We have applied them in our paper.

When the front start the propagation a perturbation is caused. In the stable region, the perturbation does not cause any visible oscillation. In the unstable region, this perturbation results in the physical instability that never diminish. In the critical limit, the oscillation is cause by perturbation damps down (Fig. \ref{776318}) as the simulation goes on and the front propagation continues.