Carbon and oxygen mass fractions for mixed ejecta models of Sukhbold et al. (2016) as a function of the progenitor ZAMS mass (MZAMS). The orange and red dots represent the 12C and 16O mass fractions, respectively, which do not vary significantly in the innermost 0.1 M⊙ of ejecta (see Figure 7). Progenitors with MZAMS = 8–12 M⊙ have comparable mass fractions of carbon and oxygen that are consistent with the observed line intensities in Kes 75.