Temporal evolution of the fractional abundances of selected carbon-chain species in the two-phase model simulated with the RE approach and the macroscopic MC method. RE represents the rate equation calculation and MC represents the macroscopic Monte Carlo simulation. The two-phase model adopts different t_cold, t_cold = 10⁵ yr in the two-phase model A while t_cold = 3 × 10⁵ yr in the two-phase model B. The temporal evolution of the temperature T is also plotted in the figure.