Abundance ratios calculated from the stellar yields of Woosley & Weaver (1995). Yields are plotted for two mass ranges, 11–25 M_⊙ (open symbols) and 30–40 M_⊙ (filled symbols), and two metallicities, 0.1 Z_⊙ (diamonds) and 0.01 Z_⊙ (squares). The grey stripe shows the observed values. The horizontal black line shows the average ratio observed in the H ii region of BCDs (Izotov et al. 1999).