Correlation between the average ratio of HC₃N/N₂H⁺ and the average abundance of HC₃N with respect to H₂ within four different ranges (panel A: 7 × 10³ AU, panel B: 10⁴ AU, panel C: 5 × 10⁴ AU, and panel D: 10⁵ AU) around the center by adopting model 4 in chemical simulations compared with observations. The results during the HMSC, HMPO, HMC, and UCHII stages are plotted as squares, circles, diamonds, and triangles, respectively. The evolution of HC₃N/N₂H⁺ and HC₃N/H₂ throughout t_total during each stage consistently decrease (from right to left and from top to bottom). The observations proposed by Taniguchi et al. (2019b) and Wang et al. (2023, including derived column density of HC₃N, N₂H⁺, and H₂ simultaneously) are plotted as solid squares, solid circles, and solid triangles, respectively, with error bars.