Element abundance ratios relative to O as predicted for model M4C compared to observed values of PNe and H ii regions as presented in HPCG09. The O/H abundance of H ii regions was corrected for dust depletion, as explained in Sect. 4.1. H ii regions are represented by magenta filled circles, young-PNe by green filled squares and old-PNe, by blue filled triangles. The open squares are the two type-I PNe, and the open triangle is PN6 (see text or HPCG09). The magenta filled star in the Fe/O panel represents the value derived by Venn et al. (2001) for A-type supergiants. Observed C/O value is not shown because there is no observational C/H value from CELs.