Ratios between the computed abundances of gas-phase CO (a), CH₃OH (b), H₂CO (c), N₂ (d), NH₃ (e), and HCN (f) in the Milky Way and in the SMC are plotted vs. time at grain temperatures at 10 and 30 K. The dashed horizontal line indicates the ratio of the elemental abundance of carbon ((a), (b), (c)) and nitrogen ((d), (e), (f)) between the two galaxies. The closely spaced abundance ratios of carbon and oxygen appear as one line.